Document:

Exhibit 10.12

 Exhibit 10.12 

REGISTRATION RIGHTS AGREEMENT 

This Registration Rights Agreement (the “Agreement”) is made and entered into as of this 2nd day of March 2010 by and among Square 1
Financial, Inc., a Delaware corporation (the “Corporation”) and each of the other persons executing this Agreement (each, a “Holder” and collectively, the “Holders”), and is entered into in connection with the Stock
Purchase Agreement by and among the Corporation and the Holders dated the date hereof (the “Stock Purchase Agreement”). 
 The
parties hereby agree as follows: 
 1. Certain Definitions. 

Capitalized terms used herein which are defined in the Stock Purchase Agreement shall have the meanings set forth in the Stock Purchase
Agreement, unless otherwise defined herein. As used in this Agreement, the following terms shall have the following meanings: 

“Affiliate” means, with respect to any person, any other person which directly or indirectly controls, is controlled by, or
is under common control with, such person. 
 “Business Day” means a day, other than a Saturday or Sunday, on which banks
in New York are open for the general transaction of business. 
 “Common Stock” means the Corporation’s Class A
Common Stock, par value $0.01 per share and any securities into which such shares may hereinafter be reclassified, together with the Corporation’s Class B Non-Voting Common Stock, par value $0.01 per share and any securities into which such
shares may hereinafter be reclassified. 
 “Exchange Act” means the Securities Exchange Act of 1934, as amended, and the
rules and regulations promulgated thereunder. 
 “FINRA” means the Financial Industry Regulatory Authority, Inc. 

“Prospectus” means the prospectus included in any Registration Statement (as defined below), as amended or supplemented by
any prospectus supplement, with respect to the terms of the offering of any portion of the Registrable Securities covered by such Registration Statement and by all other amendments and supplements to the prospectus, including post-effective
amendments and all material incorporated by reference in such prospectus. 
 “Purchaser” means any person which purchases
shares of Common Stock in the Private Placement and any Affiliate or permitted transferee of any such Purchaser who is a subsequent holder of any Registrable Securities. 

“Register,” “registered” and “registration” refer to a registration made by preparing and
filing a Registration Statement or similar document in compliance with the Securities Act (as defined below), and the declaration or ordering of effectiveness of such Registration Statement or document. 

  
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 “Registrable Securities” means (i) the Shares and (ii) any shares of
Common Stock issued as, or issuable upon the conversion or exercise of any warrant, right or other security that is issued as, a dividend or other distribution with respect to, or in exchange for or in replacement of, the Shares; provided, that, a
security shall cease to be a Registrable Security upon sale pursuant to a Registration Statement or pursuant to Rule 144 under the Securities Act. 

“Registration Statement” means any registration statement of the Corporation filed under the Securities Act that covers the
resale of any of the Registrable Securities pursuant to the provisions of this Agreement (including any registration statement referred to in Section 2), amendments and supplements to such Registration Statement(s), including the Prospectus,
post-effective amendments, all exhibits and all material filed and incorporated by reference in such Registration Statement. 

“Required Purchasers” means Purchasers holding a majority of the Registrable Securities. “SEC” means the U.S.
Securities and Exchange Commission. 
 “Securities Act” means the Securities Act of 1933, as amended, and the rules and
regulations promulgated thereunder. 
 “Shares” means all of the shares of Common Stock held by one or more Purchasers.

 2. Registration. 

(a) Registration Statement. 

(i) If the Corporation determines (by vote of the Corporation’s Board of Directors) to register any of its securities under the
Securities Act for sale to the public (except with respect to registration statements on Forms S-4, S-8 or another form not available for registering the Registrable Securities for sale to the public) at any time after the date of this Agreement,
each such time the Corporation will give written notice at the applicable address of record to the Purchasers of its intention to do so. Upon the written request of any person then holding Registrable Securities, given within 20 days after receipt
by the Purchasers of such notice, the Corporation will, subject to the limits contained in this Section 2, use its best efforts to cause all such Registrable Securities of the requesting Holders to be registered under the Securities Act and
qualified for sale under any state blue sky law, all to the extent required to permit such sale or other disposition of said Registrable Securities; provided, however, that (A) if the Corporation is advised in writing in good faith by any
managing underwriter of the Corporation’s securities being offered in a public offering pursuant to such Registration Statement that the amount to be sold by persons other than the Corporation (collectively, “Selling Stockholders”) is
greater than the amount which can be offered without adversely affecting the offering, the Corporation may reduce the amount offered for the accounts of Selling Stockholders (including such Holders of shares of Registrable Securities) to a number
deemed satisfactory by such managing underwriter; and (B) (1) in no event shall the amount of Registrable Securities of selling Purchasers be reduced below 10% of the total amount of securities included in such offering; and (2) any
shares to be excluded shall be determined in the following order of priority: (a) securities held by any person not having any contractual, incidental registration rights, (b) securities held by any person having contractual, incidental

  
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registration rights pursuant to an agreement which is not this Agreement, and (c) the Registrable Securities sought to be included by the Holders thereof as determined on a pro rata basis
(based upon the aggregate number of Registrable Securities held by such holders). 
 (ii) At any time after 180 days after the closing of
the initial public offering of the Common Stock pursuant to an effective registration under the Securities Act, one or more Purchasers, provided that the Purchasers collectively hold at least 10% of the Registrable Securities, may notify the
Corporation that they intend to offer or cause to be offered for public sale all or any portion of their Registrable Securities in the manner specified in such request. Such request may specify that the Corporation register Registrable Securities on
a shelf registration statement (a “Shelf Registration Statement”) on Form S-3 that contains a prospectus in such form as to permit the Purchasers to sell all such Registrable Securities at any time beginning on or after the effective date
thereof pursuant to Rule 415 under the Securities Act at any time which the Corporation is eligible to use such Shelf Registration Statement, and any such Shelf Registration Statement shall in all events and notwithstanding any other provision of
this Agreement register all Registrable Securities. Upon receipt of a request for registration, the Corporation shall promptly deliver notice of such request to all Purchasers holding Registrable Securities specifying the method of registration, who
shall then have 30 days to notify the Corporation in writing of their desire to be included in such registration if such registration request does not relate to a Shelf Registration Statement. If the request for registration contemplates an
underwritten public offering, Corporation shall state such in the written notice and in such event the right of any person to participate in such registration (other than a registration on a Shelf Registration Statement) shall be conditioned upon
such person’s participation in such underwritten public offering and the inclusion of such person’s Registrable Securities in the underwritten public offering to the extent provided herein. If at any time following the filing of any Shelf
Registration Statement, Purchasers that collectively hold at least 10% of the Registrable Securities desire to sell all or any portion of the Registrable Securities under such Shelf Registration Statement pursuant to an underwritten offering (an
“Underwritten Takedown”), they will so notify the Corporation of such intention at least 15 days prior to any such sale, and the Corporation shall provide notice of such intended Underwritten Takedown to all Purchasers holding Registrable
Securities specifying the method of registration, who shall then have 10 days to notify the Corporation in writing of their desire to have their Registrable Securities included in such Underwritten Takedown. 

(iii) The Corporation will use its best efforts to expeditiously effect the registration under the Securities Act of all Registrable
Securities whose Holders request participation in such registration; provided, however, that the Corporation shall not be required to effect registration pursuant to a request under this Section 2 more than once for the Holders of the
Registrable Securities as a group if the Corporation has registered all Registrable Securities on a Shelf Registration Statement; otherwise, the Corporation shall not be required to effect registration pursuant to a request under this Section 2
more than two times for the holders of Registrable Securities as a group. Notwithstanding anything to the contrary contained herein, no request may be made under this Section 2 within 90 days after the effective date of a registration statement
filed by the Corporation covering a firm commitment underwritten public offering in which the holders of Registrable Securities shall have been entitled to join pursuant to Section 2(a)(iv) or demand pursuant to Section 2(a)(i) and in
which there shall have been registered all Registrable Securities as to which registration shall have been requested. A registration will not 

  
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count as a requested registration under Section 2(a)(ii) unless no more than 20% of the Registrable Securities requested to be included in such Registration Statement are not included
pursuant to Section 2(a)(iv) below, and (B) unless and until the Registration Statement relating to such registration has been declared effective by the SEC at the request of the initiating shareholders; provided, however, that a majority
in interest of the participating Holders of Registrable Securities may request, in writing, that the Corporation withdraw a Registration Statement which has been filed under Section 2(a)(ii) but has not yet been declared effective, and a
majority in interest of such Holders may thereafter request the Corporation to reinstate such Registration Statement, if permitted under the Securities Act; or to file another Registration Statement, in accordance with the procedures set forth
herein and without reduction in the number of demand registrations permitted under this Section 2(a)(iii). 
 (iv) If a requested
registration pursuant to Section 2(a)(ii) involves an underwritten public offering and the managing underwriter of such offering determines in good faith that the number of securities sought to be offered should be limited due to market
conditions, then the number of securities to be included in such underwritten public offering shall be reduced to a number deemed satisfactory by such managing underwriter; provided, that the shares to be excluded shall be determined in the
following order of priority: (A) persons not having any contractual or other right to include such securities in the Registration Statement, (B) securities held by any other persons (other than the holders of Registrable Securities) having
a contractual, incidental “piggy back” right to include such securities in the Registration Statement, (C) securities to be registered by the Corporation pursuant to such Registration Statement, (D) Registrable Securities of
Holders who did not make the original request for registration and, if necessary, (E) Registrable Securities of Holders who requested such registration pursuant to Section 2(a)(ii). If there is a reduction of the number of Registrable
Securities pursuant to clauses (D) or (E), such reduction shall be made on a pro rata basis (based upon the aggregate number of Registrable Securities held by such Holders). 

(v) With respect to a request pursuant to Section 2(a)(ii) for registration which is for an underwritten public offering or for an
Underwritten Takedown, the managing underwriter shall be chosen by the holders of a majority of the Registrable Securities to be sold in such offering, subject to the consent of the Corporation which shall not be unreasonably withheld or delayed.
The Corporation may not cause any other registration of securities for sale for its own account (other than a registration effected solely to implement an employee benefit plan or a transaction to which Rule 145 of the Securities Act is applicable)
to become effective within 90 days following the effective date of any registration required pursuant to this Section 2, which is for an underwritten public offering or for an Underwritten Takedown). 

(vi) If any Registration Statement refers to any Holder by name or otherwise as the holder of any securities of the Corporation, then such
Holder shall have the right to require (a) the insertion therein of language, in form and substance reasonably satisfactory to such Holder, to the effect that the holding by such holder of such securities is not to be construed as a
recommendation by such Holder of the investment quality of the Corporation’s securities covered thereby and that such holding does not imply that such Holder will assist in meeting any future financial requirements of the Corporation, or
(b) in the event that such reference to such Holder by name or otherwise is not required by the Securities Act or any similar Federal or state securities or “blue sky” statute and the rules and regulations thereunder then in force,
deletion of the reference to such holder. 

  
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 (b) Form of Registration Statement. Unless otherwise provided herein, any such
Registration Statement referred to in this Agreement shall be on Form S-3, unless the Corporation is not then eligible to file a registration statement on Form S-3 under the Securities Act, in which case such Registration Statement shall be on Form
S-1. Such Registration Statement also shall cover, to the extent allowable under the Securities Act and the rules promulgated thereunder (including Rule 416 under the Securities Act), such indeterminate number of additional shares of Common Stock
resulting from stock splits, stock dividends or similar transactions with respect to the Registrable Securities. Such Registration Statement may include shares of Common Stock and other securities for the account of other holders without the prior
written consent of the Required Purchasers, provided that the inclusion of such shares of Common Stock or securities shall not have a material adverse effect on the offer and sale of the shares registered under such Registration Statement. The
Registration Statement (and each amendment or supplement thereto, and each request for acceleration of effectiveness thereof) shall be provided to the Purchasers and their counsel prior to its filing or other submission, and the Corporation shall
include therein the reasonable comments of the Purchasers or their counsel. 
 (c) Expenses. The Corporation will pay all expenses
incurred by it associated with any Registration Statement or incident to its performance or compliance with this Agreement, including filing and printing fees, the Corporation’s counsel and accounting fees and expenses, FINRA and filing fees of
any applicable national securities exchange, and costs associated with clearing the Registrable Securities for sale under applicable state securities laws, but the Corporation shall not be liable for fees and expenses incurred by the Purchasers
(including any Purchasers’ counsel fees), or any discounts, commissions, fees of underwriters, selling brokers, dealer managers or similar securities industry professionals with respect to the Registrable Securities being offered. 

(d) Effectiveness. 
 (i)
The Corporation shall use its best efforts to file each Registration Statement within 45 calendar days after the request by the Holders hereunder if the Registration Statement relates to a public offering of shares of Common Stock, and 60 calendar
days for any other Registration Statement, and to have each Registration Statement declared effective prior to the 60th calendar day following the date that such Registration Statement was initially filed with the SEC (the “Filing Date”)
(or, in the event the SEC reviews and has written comments to the Registration Statement, the 90th calendar day following the Filing Date) (the “Effectiveness Deadline”); provided, however, that if the Corporation is notified by the SEC
that the Registration Statement will not be reviewed or is no longer subject to further review and comments, the Effectiveness Deadline as to such Registration Statement shall be the 3rd Business Day following the date on which the Corporation is so
notified if such date precedes the dates otherwise required above, and the Corporation shall use its best efforts to keep each Registration Statement continuously effective under the Securities Act until the earlier of the following (the
“Effectiveness Period”): (A) such time as all of the Registrable Securities covered by such Registration Statement have been publicly sold by the Holders, (B) there otherwise ceases to be Registrable Securities, or (C) in
the case of a Shelf Registration Statement, three 

  
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years from the date of filing thereof; provided that if, at the expiration of such three-year period, any Registrable Securities remain outstanding, the Company shall use its best efforts to file
on the date of expiration of such three-year period a new Shelf Registration Statement. The Corporation shall notify the Purchasers by facsimile or e-mail as promptly as practicable, and in any event, within 48 hours, after (X) the Corporation
receives written comments to a Registration Statement from the SEC, (Y) the Corporation is notified by the SEC that the Registration Statement will not be reviewed or is no longer subject to further review and comments, and (Z) a
Registration Statement is declared effective. At such time as the Corporation notifies the Purchasers that a Registration Statement is declared effective as provided in the immediately preceding sentence, the Corporation shall simultaneously provide
the Purchasers with copies of any related Prospectus to be used in connection with the sale or other disposition of the securities covered thereby. 

(ii) For not more than 40 consecutive calendar days or for a total of not more than 75 calendar days (which need not be consecutive days) in
any 12-month period, the Corporation may delay the disclosure of material non-public information concerning the Corporation, by deferring the filing of any Registration Statement as otherwise required under this Section 2, or suspending the use
of any Prospectus included in any registration contemplated by this Section, if such disclosure at the time is not, in the good faith opinion of the Corporation, in the best interests of the Corporation (an “Allowed’ Delay”);
provided, that the Corporation shall promptly (a) notify the Purchasers in writing of the existence of (but in no event, without the prior written consent of a Purchaser, shall the Corporation disclose to such Purchaser any of the facts or
circumstances regarding) an Allowed Delay, (b) advise the Purchasers in writing to cease all sales under the Registration Statement until the end of the Allowed Delay, and (c) use its best efforts to terminate an Allowed Delay as promptly
as practicable. 
 (e) Certain Events. If: (i) a Registration Statement requested pursuant to Section 2(a)(ii) is not filed with
the SEC on or prior to the 30th day after the date one or more Purchasers delivered notice to the Corporation of their intent to offer or cause to be offered for public sale all or any portion of their Registrable Securities, or (ii) a
Registration Statement that has been filed with the SEC as contemplated under Section 2(a)(i) or Section 2(a)(ii) is not declared effective by the SEC (or otherwise does not become effective) for any reason on or prior to the Effectiveness
Deadline, or (iii) after its effective date, (A) such Registration Statement ceases for any reason (including without limitation by reason of a stop order, or the Corporation’s failure to update the Registration Statement), to remain
continuously effective as to all Registrable Securities included in such Registration Statement or (B) the Holders are not permitted to utilize the Prospectus therein to resell such Registrable Securities (x) pursuant to
Section 3(a)(xiii) or (y) because of an Allowed Delay and the 40 consecutive calendar- or 75 calendar-day periods set forth in Section 2(d)(ii) above have been exceeded, or (iv) the Corporation fails to satisfy the current public
information requirement pursuant to Rule 144(c) as a result of which the Holders are unable to sell Registrable Securities without restriction (other than volume limitations, manner of sale restrictions and notice filing requirements that may apply
if the Holder is an “affiliate” of the Corporation, as that term is defined in Rule 144(a)(1)) under Rule 144 (or any successor thereto), (any such failure or breach in clauses (i) through (iv) above being referred to as an
“Event,” and, for purposes of clauses (i), (ii) or (iv), the date on which such Event occurs, or for purposes of clause (iii), the date on which such 40 consecutive calendar-day or 75 calendar-day period is exceeded, being referred to
as an “Event Date”), then 

  
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in addition to any other rights the Holders may have hereunder or under applicable law, on each such Event Date and on each monthly anniversary of each such Event Date (if the applicable Event
shall not have been cured by such date) until the earlier of (1) the applicable Event is cured or (2) the Registrable Securities are eligible for resale pursuant to Rule 144 without manner of sale or volume restrictions, the Corporation
shall pay to each Holder an amount in cash, as partial liquidated damages and not as a penalty (“Liquidated Damages”), equal to 1.0% of the aggregate purchase price paid by such Holder pursuant to the Stock Purchase Agreement for any
unregistered Registrable Securities held by such Holder on the Event Date. The parties agree that notwithstanding anything to the contrary herein or in the Stock Purchase Agreement, no Liquidated Damages shall be payable with respect to any period
after the expiration of the Effectiveness Period (except in respect of an Event described in Section 2(e)(iv) herein) (it being understood that this sentence shall not relieve the Corporation of any Liquidated Damages accruing prior to the
Effectiveness Deadline) and in no event shall the aggregate amount of Liquidated Damages (excluding Liquidated Damages payable in respect of an Event described in Section 2(e)(iv) herein) payable to a Holder exceed, in the aggregate, 6% of the
aggregate purchase price paid by such Holder pursuant to the Stock Purchase Agreement (12% in respect of an Event described in Section 2(e)(iv) herein). If the Corporation fails to pay any Liquidated Damages pursuant to this Section in full
within 5 Business Days after the date payable, the Corporation will pay interest thereon at a rate of 1.0% per month (or such lesser maximum amount that is permitted to be paid by applicable law) to the Holder, accruing daily from the date such
Liquidated Damages are due until such amounts, plus all such interest thereon, are paid in full. The Liquidated Damages pursuant to the terms hereof shall apply on a daily pro-rata basis for any portion of a month prior to the cure of an Event,
except in the case of the first Event Date. 
 3. Corporation Obligations. 

(a) The Corporation will use its best efforts to effect the registration of the Registrable Securities in accordance with the terms hereof,
and pursuant thereto the Corporation will (but subject to Section 2(d)(ii)): 
 (i)(A) promptly furnish to the Purchasers, copies of
all such documents proposed to be filed, which documents will be subject to the review of such Purchasers, and (B) cause its officers and directors, counsel and independent certified public accountants to respond to such inquiries as shall be
necessary, to conduct a reasonable review of such documents. The Corporation shall not file the Registration Statement or any such Prospectus of any amendments or supplements thereto to which the holders of a majority of the Registrable Securities
shall object in writing within 3 Business Days of their receipt thereof if: (1) such objection relates specifically to any description in the Registration Statement, Prospectus or amendment or supplement thereto of the Purchasers, any Affiliate
of any Purchaser (other than the Corporation if the Corporation is an Affiliate of any Purchaser) or the Shares, or (2) the Shares, the resale of which is covered by the Registration Statement, Prospectus, amendment or supplement, represent
more than 50% of all shares of Common Stock, the sale and/or resales of which are covered by such Registration Statement, Prospectus, amendment or supplement. 

  
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 (ii) respond promptly to any comments received from the SEC with respect to the Registration
Statement or any amendment thereto and as promptly as possible provide the Purchasers true and complete copies of all correspondence from and to the SEC relating to the Registration Statement. 

(iii) notify the Purchasers promptly (and, in the case of (A)(1) below, not less than 3 days prior to such filing) and (if requested by any
such Person) confirm such notice in writing no later than 2 Business Days following the day (A)(1) when a Prospectus or any Prospectus supplement or post-effective amendment to the Registration Statement is filed; (2) when the SEC notifies the
Corporation whether there will be a “review” of such Registration Statement and whenever the SEC provides comments in writing or orally on such Registration Statement and (3) with respect to the Registration Statement or any
post-effective amendment, when the same has become effective; (B) of any request by the SEC or any other Federal or state governmental authority for amendments or supplements to the Registration Statement or Prospectus or for additional
information; (C) of the issuance by the SEC of any stop order suspending the effectiveness of the Registration Statement covering any or all of the Registrable Securities or the initiation or threatening of any Proceedings for that purpose;
(D) if at any time any of the representations and warranties of the Corporation contained in any agreement contemplated hereby cease to be true and correct in all material respects; (E) of the receipt by the Corporation of any notification
with respect to the suspension of the qualification or exemption from qualification of any of the Registrable Securities for sale in any jurisdiction, or the initiation of any Proceeding for such purpose; and (F) of the occurrence of any event
that makes any statement made in the Registration Statement or Prospectus or any document incorporated or deemed to be incorporated therein by reference untrue in any material respect or that requires any revisions to the Registration Statement,
Prospectus or other documents so that, in the case of the Registration Statement or the Prospectus, as the case may be, it will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or
necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. 
 (iv) if
requested by the Required Purchasers, (i) promptly incorporate in a Prospectus supplement or post-effective amendment to the Registration Statement such information as the Corporation reasonably agrees should be included therein and
(ii) make all required filings of such Prospectus supplement or such post-effective amendment as soon as practicable after the Corporation has received notification of the matters to be incorporated in such Prospectus supplement or
post-effective amendment. 
 (v) promptly deliver to each Purchaser, without charge, as many copies of the Prospectus or Prospectuses
(including each form of prospectus) and each amendment or supplement thereto as such Persons may reasonably request. 
 (vi)(i) furnish to
each Purchaser a signed counterpart, addressed to the Purchaser, of an opinion of counsel for the Corporation, dated the effective date of the Registration Statement, and (ii) subject only to the obligation of the Corporation to use its best
efforts, furnish to each Purchaser a “comfort” letter signed by the independent public accountants who have certified the Corporation’s financial statements included in the Registration Statement, covering substantially the same
matters with respect to the Registration Statement (and the 

  
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prospectus included therein) and (in the case of the accountants’ letter) with respect to events subsequent to the date of the financial statements, as are customarily covered (at the time
of such registration) in opinions of the Corporation’s counsel and in accountants’ letters delivered to the underwriters in underwritten public offerings of securities; 

(vii) cooperate with the Purchasers to facilitate the timely preparation and delivery of certificates representing Registrable Securities to
be sold pursuant to a Registration Statement, which certificates, to the extent permitted by applicable federal and state securities laws, shall be free of all restrictive legends, and to enable such Registrable Securities to be in such
denominations and registered in such names as any Purchaser may request in connection with any sale of Registrable Securities; 
 (viii)
prepare and file with the SEC such amendments and post-effective amendments to the Registration Statement and the Prospectus as may be necessary to keep the Registration Statement effective for the Effectiveness Period and to comply with the
provisions of the Securities Act and the Exchange Act with respect to the distribution of all of the Registrable Securities covered thereby in accordance with the intended method of disposition as set forth in the Registration Statement, Prospectus
or Prospectus supplement; 
 (ix) correct any deficiency (in the judgment of either the Corporation or the Holders) between the preliminary
prospectus and the final prospectus, and pay any expenses associated with the recirculation of the final prospectus following the correction of such deficiency; 

(x) use its best efforts to (i) prevent the issuance of any stop order or other suspension of effectiveness or qualification or
exemption of qualification and, (ii) if such order is issued, obtain the prompt withdrawal of any such order; 
 (xi) prior to any
public offering of Registrable Securities, use reasonable best efforts to register or qualify or cooperate with the Purchasers and their counsel in connection with the registration or qualification of such Registrable Securities for offer and sale
under the securities or blue sky laws of such jurisdictions requested by the Purchasers, to keep such registration or qualification effective during the Effectiveness Period and do any and all other acts or things necessary or advisable to enable
the distribution in such jurisdictions of the Registrable Securities covered by the Registration Statement; provided, however, that the Corporation shall not be required in connection therewith or as a condition thereto to (i) qualify to do
business in any jurisdiction where it would not otherwise be required to qualify but for this Section 3, (ii) subject itself to general taxation in any jurisdiction where it would not otherwise be so subject but for this Section 3, or
(iii) file a general consent to service of process in any such jurisdiction; 
 (xii) use its best efforts to cause all Registrable
Securities covered by a Registration Statement to be listed on each securities exchange, interdealer quotation system or other market on which similar securities issued by the Corporation are then listed; 

(xiii) promptly notify the Purchasers, at any time when a Prospectus relating to Registrable Securities is required to be delivered under the
Securities Act (including 

  
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during any period when the Corporation is in compliance with Rule 172), upon discovery that, or upon the happening of any event as a result of which, the Registration Statement (including the
Prospectus), as then in effect, includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing,
and at the request of any such holder, promptly prepare, file with the SEC pursuant to Rule 172 and furnish to such holder a supplement to or an amendment of such Prospectus or post-effective amendment to such Registration Statement (and have it
declared effective as promptly as practicable) as may be necessary so that such Prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements
therein not misleading in light of the circumstances then existing; 
 (xiv) otherwise use its best efforts to comply with all applicable
rules and regulations of the SEC under the Securities Act and the Exchange Act, including Rule 172, notify the Purchasers promptly if the Corporation no longer satisfies the conditions of Rule 172 and take such other actions as may be reasonably
necessary to facilitate the registration of the Registrable Securities hereunder; and make available to its security holders, as soon as reasonably practicable, but not later than the Availability Date (as defined below), an earning statement
covering a period of at least 12 months, beginning after the effective date of each Registration Statement, which earning statement shall satisfy the provisions of Section 11(a) of the Securities Act, including Rule 158 promulgated thereunder
(for the purpose of this Section 3, “Availability Date” means the 45th day following the end of the fourth fiscal quarter that includes the effective date of such Registration Statement, except that, if such fourth fiscal quarter is
the last quarter of the Corporation’s fiscal year, “Availability Date” means the 90th day after the end of such fourth fiscal quarter); 

(xv) upon written notice from a Purchaser that such Purchaser has a legal obligation to make a filing with the FINRA Corporate Financing
Department pursuant to FINRA Rule 5110 with respect to the public offering contemplated by the Registration Statement (an “Issuer Filing”), the Corporation agrees it will effect such filing prior to the later to occur of five Trading Days
after receipt of the written notice and one Trading Day after the date that the Registration Statement is first filed with the SEC. The Corporation shall use reasonable best efforts to pursue the Issuer Filing until the FINRA issues a letter
confirming that it does not object to the terms of the offering contemplated by the Registration Statement. The Corporation will pay any filing fees and expenses in connection with the Issuer Filing; 

(xvi) in any underwritten offering, including any Underwritten Take-Down Transaction: 

(A) If requested by the underwriters, the Corporation shall enter into an underwriting agreement with the underwriters for such offering, such
agreement to be reasonably satisfactory in substance and form to the underwriters and the Holders of Registrable Securities participating in such underwritten offering; and 

(B) cause its officers and employees to participate in, and to otherwise facilitate and cooperate with the preparation of the Registration
Statement and prospectus and any amendments or supplements thereto (including participating in meetings, drafting sessions and 

  
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due diligence sessions) and to prepare for, and participate in “road shows,” and all such other customary selling efforts as the Holders of a majority of the Registrable Securities
participating in such offering or the underwriters reasonably request in order to expedite or facilitate such disposition but in each case taking into account the Corporation’s business needs; provided that, notwithstanding anything to the
contrary herein, the total number of “road shows” the Corporation shall be required to participate in pursuant to this Agreement shall not exceed two in each case; 

(b) With a view to making available to the Purchasers the benefits of Rule 144 (or its successor rule) and any other rule or regulation of the
SEC that may at any time permit the Purchasers to sell shares of Common Stock to the public without registration, the Corporation covenants and agrees to: make and keep public information available, as those terms are understood and defined in Rule
144, until such date as all of the Registrable Securities shall have been resold; (ii) file with the SEC in a timely manner all reports and other documents required of the Corporation under the Exchange Act; and (iii) furnish to each
Purchaser upon request, as long as such Purchaser owns any Registrable Securities, (A) a written statement by the Corporation that it has complied with the reporting requirements of the Exchange Act, and (B) such other information as may
be reasonably requested in order to avail such Purchaser of any rule or regulation of the SEC that permits the selling of any such Registrable Securities without registration. 

(c) With a view to satisfying its obligations under Section 2(a), the Corporation, after the first public offering of its securities
registered under the Securities Act, shall use its best efforts to qualify and remain qualified to register securities pursuant to a registration statement and Form S-3 under the Securities Act. 

4. Due Diligence Review; Information. 

(a) Subject to paragraph (b) of this Section 4, upon reasonable prior notice, the Corporation shall make available, during normal
business hours, for inspection and review by the Purchasers, advisors to and representatives of the Purchasers (who may or may not be affiliated with the Purchasers and who are reasonably acceptable to the Corporation), and to the underwriters for
any underwritten offering chosen pursuant to Section 2(a)(v), all financial and other records, all filings with the SEC, and all other corporate documents and properties of the Corporation as may be reasonably necessary for the purpose of such
review, and cause the Corporation’s officers, directors, employees and independent accountants, within a reasonable time period, to supply all such information reasonably requested by the Purchasers or any such representative, advisor or
underwriter in connection with such Registration Statement (including, without limitation, in response to all questions and other inquiries reasonably made or submitted by any of them), prior to and from time to time after the filing and
effectiveness of the Registration Statement for the sole purpose of enabling the Purchasers and such representatives, advisors and underwriters and their respective accountants and attorneys to conduct initial and ongoing due diligence with respect
to the Corporation and the accuracy of such Registration Statement. 
 (b) Beginning with the filing of the Registration Statement in
connection with the Corporation’s initial public offering of Common Stock or, if earlier, the date when the 

  
 11 

 
Corporation first becomes subject to the reporting provisions under the Exchange Act applicable to issuers of securities, the Corporation shall not disclose material nonpublic information to the
Purchasers, or to advisors to or representatives of the Purchasers, unless prior to disclosure of such information the Corporation identifies such information as being material nonpublic information and provides the Purchasers, such advisors and
representatives with the opportunity to accept or refuse to accept such material nonpublic information for review and any Purchaser wishing to obtain such information enters into an appropriate confidentiality agreement with the Corporation with
respect thereto. 
 5. Obligations of the Purchasers. 

(a) Each Purchaser shall promptly furnish in writing to the Corporation such information regarding itself, the Registrable Securities held by
it and the intended method of disposition of the Registrable Securities held by it, as shall be reasonably required to effect the registration of such Registrable Securities and shall execute such documents in connection with such registration as
the Corporation may reasonably request. At least 10 Business Days prior to the first anticipated filing date of the Registration Statement, the Corporation shall notify each Purchaser of the information the Corporation requires from such Purchaser
if such Purchaser elects to have any of the Registrable Securities included in the Registration Statement. A Purchaser shall provide such information to the Corporation at least 3 Business Days prior to the first anticipated filing date of such
Registration Statement if such Purchaser elects to have any of the Registrable Securities included in the Registration Statement. 
 (b)
Each Purchaser, by its acceptance of the Registrable Securities, agrees to cooperate with the Corporation as reasonably requested by the Corporation in connection with the preparation and filing of a Registration Statement hereunder, unless such
Purchaser has notified the Corporation in writing of its election to exclude all of its Registrable Securities from such Registration Statement. 

(c) Each Purchaser agrees that, upon receipt of any notice from the Corporation of either (i) the commencement of an Allowed Delay
pursuant to Section 2(d)(ii) or (ii) the happening of an event pursuant to Section 3(a)(xiii) hereof, such Purchaser will immediately discontinue disposition of Registrable Securities pursuant to the Registration Statement covering
such Registrable Securities until the Purchaser is advised by the Corporation that a supplemented or amended prospectus has been filed with the SEC and until any related post-effective amendment is declared effective and, if so directed by the
Corporation, the Purchaser shall deliver to the Corporation or destroy (and deliver to the Corporation a certificate of destruction) all copies in the Purchaser’s possession of the Prospectus covering the Registrable Securities current at the
time of receipt of such notice. 
 6. Indemnification. 

(a) Indemnification by the Corporation. The Corporation will indemnify and hold harmless each Purchaser and its officers, directors,
members, partners, employees, attorneys and agents, successors and assigns, and each other person, if any, who controls such Purchaser within the meaning of the Securities Act or Section 20 of the Exchange Act (and its officers, directors,
partners, members and employees), against any losses, claims, damages, expenses, 

  
 12 

 
costs (including reasonable attorney fees) or liabilities, joint or several, to which they may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages,
expenses, costs or liabilities (or actions in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement of any material fact contained in the Registration Statement, any preliminary prospectus or
final prospectus contained therein, or form of prospectus or any amendment or supplement thereof; (ii) the omission or alleged omission to state in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or
form of prospectus or any amendment or supplement thereof, a material fact required to be stated therein or necessary to make the statements therein not misleading; (iii) any violation or alleged violation by the Corporation or its agents of
the Securities Act or any state securities law, or any rule or regulation thereunder in connection with such registration; or (iv) any failure to register or qualify the Registrable Securities included in any such Registration in any state
where the Corporation or its agents has affirmatively undertaken or agreed in writing that the Corporation will undertake such registration or qualification on a Purchaser’s behalf, and will reimburse such Purchaser, and each such officer,
director or member and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that the Corporation
will not be liable in any such case if and to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission so made in conformity with
information furnished by such Purchaser or any such controlling person in writing specifically for use in such Registration Statement or Prospectus. 

(b) Indemnification by the Purchasers. Each Purchaser agrees, severally but not jointly, to indemnify and hold harmless, to the fullest
extent permitted by law, the Corporation, its directors, officers, employees, stockholders and each person who controls the Corporation (within the meaning of the Securities Act) against any losses, claims, damages, liabilities and reasonable
expense (including reasonable attorney fees) resulting from any untrue statement of a material fact contained in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or form of prospectus or any amendment or
supplement thereof or any omission of a material fact required to be stated in the Registration Statement, any preliminary prospectus or final prospectus contained therein, or form of prospectus or any amendment or supplement thereof or necessary to
make the statements therein, in light of the circumstances under which they were made, not misleading, to the extent, but only to the extent that such untrue statement is, and such omission is not, contained in any information furnished in writing
by such Purchaser to the Corporation specifically for inclusion in such Registration Statement or Prospectus. The liability of any Purchaser for indemnification under this Section 6(b) in its capacity as a seller of Registrable Securities shall
not exceed the lesser of (i) that proportion of the total of such losses, claims, damages, expenses or liabilities indemnified against equal to the proportion of the total securities sold under such Registration Statement held by such
Purchaser, and (ii) the amount equal to the net proceeds to such Purchaser of the securities sold in any such registration; provided that no Holder shall be required to indemnify any person against any liability arising from any untrue or
misleading statement or omission contained in any preliminary prospectus if such deficiency is corrected in the final prospectus or for any liability which arises out of the failure of any person to deliver a prospectus as required by the Securities
Act. 

  
 13 

 (c) Conduct of Indemnification Proceedings. Any person entitled to indemnification
hereunder shall (i) give prompt notice to the indemnifying party of any claim with respect to which it seeks indemnification and (ii) permit such indemnifying party to assume the defense of such claim with counsel reasonably satisfactory
to the indemnified party; provided that any person entitled to indemnification hereunder shall have the right to employ separate counsel and to participate in the defense of such claim, but the fees and expenses of such counsel shall be at the
expense of such person unless (A) the indemnifying party has agreed to pay such fees or expenses, or (B) the indemnifying party shall have failed to assume the defense of such claim and employ counsel reasonably satisfactory to such person
or (C) in the reasonable judgment of any such person, based upon written advice of its counsel, a conflict of interest exists between such person and the indemnifying party with respect to such claims (in which case, if the person notifies the
indemnifying party in writing that such person elects to employ separate counsel at the expense of the indemnifying party, the indemnifying party shall not have the right to assume the defense of such claim on behalf of such person); and provided,
further, that the failure of any indemnified party to give notice as provided herein shall not relieve the indemnifying party of its obligations hereunder, except to the extent that such failure to give notice shall materially adversely affect the
indemnifying party in the defense of any such claim or litigation. It is understood that the indemnifying party shall not, in connection with any proceeding in the same jurisdiction, be liable for fees or expenses of more than one separate firm of
attorneys at any time for all such indemnified parties. No indemnifying party will, except with the consent of the indemnified party, consent to entry of any judgment or enter into any settlement that does not include as an unconditional term
thereof the giving by the claimant or plaintiff to such indemnified party of a release from all liability in respect of such claim or litigation, does not impose any injunction or similar restriction on such indemnified party and does not include a
statement as to or an admission of fault, liability, culpability or failure to act with respect to any law by an indemnified party. 
 (d)
Contribution. If for any reason the indemnification provided for in the preceding paragraphs (a) and (b) of this Section 6 is unavailable to an indemnified party or insufficient to hold it harmless, other than as expressly
specified therein, then the indemnifying party shall contribute to the amount paid or payable by the indemnified party as a result of such loss, claim, damage or liability in such proportion as is appropriate to reflect the relative fault of the
indemnified party and the indemnifying party, as well as any other relevant equitable considerations. The relative fault of such indemnifying party and indemnified party shall be determined by reference to, among other things, whether any action in
question, including any untrue or alleged untrue statement of a material fact or omission or alleged omission of a material fact, has been taken or made by, or relates to information supplied by, such indemnifying party or indemnified party, and the
parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such action, statement or omission. The parties hereto agree that it would not be just and equitable if contribution pursuant to this section were
determined by pro rata allocation or by any other method of allocation that does not take into account the foregoing equitable considerations. Notwithstanding the forgoing, a holder of Registrable Securities shall not be required to contribute under
this Section 6(d) in excess of the lesser of (i) that proportion of the total liability indemnified against equal to the proportion of the total Registrable Securities sold under such Registration Statement by such holder and (ii) the
net proceeds received by such holder from its sale of Registrable Securities under such Registration 

  
 14 

 
Statement. No Person found guilty of fraudulent representation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person not found guilty
of such fraudulent misrepresentation. 
 7. Miscellaneous. 

(a) Market Stand-Off. 

(i) Each Holder shall, if so requested by the Corporation and an underwriter of Registrable Securities in connection with any public offering
of shares of Common Stock, not directly or indirectly offer, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant for the sale of or otherwise dispose of or
transfer any shares held by it for such period, not to exceed (A) 180 days following the effective date of the relevant registration statement filed under the Securities Act in connection with the Corporation’s initial public offering of
Common Stock, or (B) 90 days following the effective date of the relevant registration statement in connection with any other public offering of Common Stock, as such underwriter shall specify reasonably and in good faith, provided, however,
that (1) all officers and directors of the Corporation and all holders of more than 5% of the outstanding shares of Common Stock (determined on a fully diluted basis) enter into agreements with terms that include provisions substantially
similar to, and each such agreement is in total consistent with, this Section 7(a)(i), (2) the Corporation uses reasonable efforts to have all holders of 25,000 or more of the outstanding shares of Common Stock (determined on a fully
diluted basis) enter into agreements with terms that include provisions similar to, and each such agreement is in total consistent with, this Section 7(a)(i), (3) if at any time the Corporation grants any of its officers or directors a
waiver of any term of any such agreement, the Corporation shall at such time grant a waiver of similar terms applicable to all other holders of Common Stock who have entered into agreements with terms that include provisions similar to this
Section 7(a)(i), including the Purchasers, with all such waivers to apply to the affected Common Stock on a pro rata basis (based upon the aggregate number of Registrable Securities held by such Holders), and (4) the limitations applicable
to each Holder in this Section 7(a)(i) only shall apply to those equity interests in the Corporation held by such Holder immediately prior to the public offering. 

(ii) The Corporation shall not effect any public sale or distribution of its equity securities, or any securities convertible into or
exchangeable or exercisable for such securities, during the seven days prior to and during the 180-day period beginning on the effective date of any registration (except as part of such underwritten registration or pursuant to registrations on Form
S-4 or S-8 or any successor form). 
 (b) Registration and Reports Under the Exchange Act. In the event that the Corporation
(i) registers a class of securities under Section 12 of the Exchange Act or (ii) shall commence to file reports under Section 13 or 15(d) of the Exchange Act, the Corporation will use its best efforts thereafter to file with the
SEC such information as is required under the Exchange Act for so long as there are holders of Registrable Securities; and in such event, the Corporation shall use its best efforts to take all action as may be required as a condition to the
availability of Rule 144 under the Securities Act (or any comparable successor rules). The Corporation shall furnish to any holder of Registrable Securities upon request a written statement 

  
 15 

 
executed by the Corporation as to the steps it has taken to comply with the current public information requirement of Rule 144 (or such comparable successor rules). After the occurrence of the
first underwritten public offering of Common Stock of the Corporation pursuant to an offering registered under the Securities Act on Form S-1 (or any comparable successor forms), subject to the limitations on transfers imposed by this Agreement, the
Corporation shall use its best efforts to facilitate and expedite transfers of Registrable Securities pursuant to Rule 144 under the Securities Act, which efforts shall include timely notice to its transfer agent to expedite such transfers of
Registrable Securities. 
 (c) Amendments and Waivers. This Agreement may be amended, modified or waived only by a writing signed by
the Corporation and the Required Purchasers. 
 (d) Notices. All notices and other communications provided for or permitted hereunder
shall be made as set forth in Section 6.3 of the Stock Purchase Agreement. 
 (e) Assignments and Transfers by Purchasers. The
provisions of this Agreement shall be binding upon and inure to the benefit of the Purchasers and their respective successors and assigns. A Purchaser may transfer or assign, in whole or from time to time in part, to one or more persons its rights
hereunder in connection with the transfer of Registrable Securities by such Purchaser to such person, provided that (i) (A) such person is an Affiliate of such Purchaser or (B) immediately upon completion of any such transfer, the
transferee holds at least 5% of the Registrable Securities, (ii) such Purchaser complies with all laws applicable thereto and provides written notice of assignment to the Corporation promptly after such assignment is effected and (iii) the
transferee agrees in writing to be bound by this Agreement as if it were a party hereto. 
 (f) Assignments and Transfers by the
Corporation. 
 (i) This Agreement may not be assigned by the Corporation (whether by operation of law or otherwise) without the prior
written consent of the Required Purchasers, provided, however, that the Corporation may assign its rights and delegate its duties hereunder to any surviving or successor corporation in connection with a merger or consolidation of the Corporation
with another corporation, or a sale, transfer or other disposition of all or substantially all of the Corporation’s assets to another corporation, without the prior written consent of the Required Purchasers, after notice duly given by the
Corporation to each Purchaser. 
 (ii) Other than transferees of Registrable Securities under Section 7(e)(i), the Corporation shall
not, without the prior written consent of holders of at least a 80% of the Registrable Securities, allow purchasers of the Corporation’s securities to become a party to this Agreement. 

(g) Benefits of the Agreement. The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the
respective permitted successors and assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies,
obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement. 

  
 16 

 (h) Counterparts; Faxes. This Agreement may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed via facsimile, which shall be deemed an original. 

(i) Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement. 
 (j) Severability. Any provision of this Agreement that is prohibited or unenforceable
in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof but shall be interpreted as if it were written so as to be enforceable to
the maximum extent permitted by applicable law, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction. To the extent permitted by applicable law, the
parties hereby waive any provision of law which renders any provisions hereof prohibited or unenforceable in any respect. 
 (k) Further
Assurances. The parties shall execute and deliver all such further instruments and documents and take all such other actions as may reasonably be required to carry out the transactions contemplated hereby and to evidence the fulfillment of the
agreements herein contained. 
 (l) Entire Agreement. This Agreement is intended by the parties as a final expression of their
agreement and intended to be a complete and exclusive statement of the agreement and understanding of the parties hereto in respect of the subject matter contained herein. This Agreement supersedes all prior agreements and understandings between the
parties with respect to such subject matter. 
 (m) Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This Agreement
shall be governed by, and construed in accordance with, the internal laws of the State of Delaware without regard to the choice of law principles thereof. Each of the parties hereto irrevocably submits to the exclusive jurisdiction of the courts of
the State of Delaware for the purpose of any suit, action, proceeding or judgment relating to or arising out of this Agreement and the transactions contemplated hereby. Service of process in connection with any such suit, action or proceeding may be
served on each party hereto anywhere in the world by the same methods as are specified for the giving of notices under this Agreement. Each of the parties hereto irrevocably consents to the jurisdiction of any such court in any such suit, action or
proceeding and to the laying of venue in such court. Each party hereto irrevocably waives any objection to the laying of venue of any such suit, action or proceeding brought in such courts and irrevocably waives any claim that any such suit, action
or proceeding brought in any such court has been brought in an inconvenient forum. EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT TO THIS AGREEMENT AND REPRESENTS THAT COUNSEL HAS BEEN CONSULTED
SPECIFICALLY AS TO THIS WAIVER. 

  
 17 

 (n) Obligations of Purchasers. The Corporation acknowledges that the obligations of each
Purchaser under this Agreement are several and not joint with the obligations of any other Purchaser, and no Purchaser shall be responsible in any way for the performance of the obligations of any other Purchaser under this Agreement. The decision
of each Purchaser to enter into to this Agreement has been made by such Purchaser independently of any other Purchaser. The Corporation further acknowledges that nothing contained in this Agreement, and no action taken by any Purchaser pursuant
hereto, shall be deemed to constitute the Purchasers as a partnership, an association, a joint venture or any other kind of entity, or create a presumption that the Purchasers are in any way acting in concert or as a group with respect to such
obligations or the transactions contemplated hereby. Each Purchaser shall be entitled to independently protect and enforce its rights, including without limitation, the rights arising out of this Agreement, and it shall not be necessary for any
other Purchaser to be joined as an additional party in any proceeding for such purpose. 
 Each Purchaser has been represented by its own
separate legal counsel in their review and negotiation of this Agreement and with respect to the transactions contemplated hereby. 

[Signature pages follow] 

  
 18 

 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first above written. 
  

					
	The Corporation	 	SQUARE 1 FINANCIAL, INC.
			
		 	By:	 	 /s/ Richard J. Casey

		 	Name: Richard J. Casey
		 	Title:   President and Chief Executive Officer
		
	Purchaser:	 	NORTHAVEN PARTNERS, L.P.
			
		 	By:	 	 /s/ Paul Burke

		 	Name: Paul Burke
		 	Title:   Member of the GP
		
	Purchaser:	 	NORTHAVEN PARTNERS II, L.P.
			
		 	By:	 	 /s/ Paul Burke

		 	Name: Paul Burke
		 	Title:   Member of the GP
		
	Purchaser:	 	NORTHAVEN OFFSHORE, L.P.
			
		 	By:	 	 /s/ Paul Burke

		 	Name: Paul Burke
		 	Title:   Director
		
	Purchaser:	 	NORTHAVEN CAPITAL PARTNERS, L.P.
			
		 	By:	 	 /s/ Paul Burke

		 	Name: Paul Burke
		 	Title:   Member of the GPExhibit 10.13

 Exhibit 10.13 

SQUARE 1 FINANCIAL, INC. 

STOCK PURCHASE AGREEMENT 

This STOCK PURCHASE AGREEMENT (this “Agreement”), dated as of September 26, 2012, is by and between Square 1
Financial, Inc. a Delaware corporation (the “Company”), and the entities identified on Exhibit A (referred to herein as “Purchaser” or “Purchasers”). 

WITNESSETH: 

WHEREAS, the Company proposes to conduct an offering of approximately 4,162,493 shares (the “Shares”) of its
Class A common stock, par value $0.01 per share (the “Class A Common Stock”) and Class B Non-Voting common stock, par value $0.01 per share, (the “Class B Common Stock” and collectively with the “Class A
Common Stock” the “Common Stock”) by means of a private placement (the “Private Placement”); 

WHEREAS, the Company has determined to first offer 2,998,856 of such Shares to the stockholders which are parties to the Stock Purchase
Agreement, as amended, entered into in connection with the Company’s May 21, 2010 private placement offering (the “Participation Offering”) and, following the close of the Participation Offering, to offer 1,163,637 Shares
to certain large stockholders of the Company and the Company’s directors and executive officers (“Additional Offering”), as set forth in the Term Sheet attached hereto as Annex I; 

WHEREAS, the Company has determined that the Shares offered in the Participation Offering and the Additional Offering shall be offered
at a price per share of $6.875; and 
 WHEREAS, each Purchaser has agreed, subject to the satisfaction of certain conditions to
purchase from the Company at $6.875 per share (the “Purchase Price”) the number of Shares set forth on Exhibit A. 

NOW THEREFORE, in consideration of the foregoing and the mutual covenants herein contained and other good and valuable consideration,
the parties hereto, intending to be legally bound hereby, agree as follows: 
  

	 	1	SALE AND PURCHASE OF SHARES 

 1.1 Sale and Purchase of Shares. Subject to the terms and
conditions herein provided, the Company hereby agrees to sell to each Purchaser and each Purchaser, severally and not jointly, agrees to purchase from the Company, at the Closing provided for in Section 2 hereof, a number of shares of
Class A Common Stock and Class B Common Stock as set forth on Exhibit A, determined in accordance with Section 2.2. Each Purchaser’s obligations hereunder are several and not joint obligations, and no Purchaser shall have any
liability to any person or entity for the performance or nonperformance by any other Purchaser hereunder. Each Purchaser understands and acknowledges that it has made its own review of the investment merits and risks of the Shares.; however, no such
review shall alter any representation or warranty given hereunder by the Company. 

  
 1 

 1.2 Registration Rights Agreement. Contemporaneously with the execution and delivery of
this Agreement, the parties hereto are executing and delivering a Registration Rights Agreement, substantially in the form attached hereto as Exhibit B (the “Registration Rights Agreement,” and together with this Agreement
and each other document or agreement executed in connection with the Transactions (as such term is defined in Section 4.1(k)) contemplated hereunder, the “Transaction Documents”), pursuant to which, among other things, the
Company will agree to provide certain registration rights with respect to the Shares under the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder (the “Securities Act”). 

 

	 	2	THE CLOSING. 

 2.1 Time and Place of the Closing. Subject to Section 3 hereof,
payment of the Purchase Price for and delivery of the Shares (together, the “Closing”) shall be made at the offices of Kilpatrick Townsend & Stockton LLP, or at such other place or in such other manner as may be agreed upon
by the Company and the Purchaser, on such date and time as the Purchaser and the Company shall mutually agree (such date and time of payment and delivery being herein called the “Closing Date”). 

2.2 Delivery of and Payment for the Shares. At the Closing, the Company shall issue in certificated form to the Purchaser the Shares to
be purchased by it, dated the Closing Date and bearing appropriate legends as hereinafter provided for, and registered on the books and records of the Company in the Purchaser’s name, against payment in full at the Closing of the aggregate
Purchase Price therefore by wire transfer of immediately available funds for credit to such account as the Company shall direct. The shares of Class A Common Stock and Class B Common Stock acquired by Endicott Opportunity Partners III, L.P.
(“Endicott”) at the Closing shall be allocated between Class A Common Stock and Class B Common Stock such that the aggregate number of shares of Class A Common Stock beneficially owned by Endicott, together with its affiliates
(the “Endicott Funds”), at the Closing shall not exceed 9.9% of the Company’s total issued and outstanding Class A Common Stock after giving effect to the Closing. 

 

	 	3	CONDITIONS TO CLOSING 

 3.1 Conditions to the Purchaser’s Obligations. The
obligations of each Purchaser hereunder are subject to the accuracy, as of the date hereof and on the Closing Date, of the representations and warranties of the Company contained herein, and to the performance by the Company of its obligations
hereunder and to each of the following additional terms and conditions: 
 (a) The Company shall have executed and delivered to the
Purchaser, or caused to be executed and delivered to the Purchaser, a copy of each of this Agreement and the Registration Rights Agreement; 

(b) The aggregate gross proceeds from the sale of the Shares of Common Stock in the Participation Offering, including the sale of the Shares
pursuant to the terms hereof, shall not be less than $20.5 million. 

  
 2 

 (c) The Company shall have furnished to the Purchaser a certificate, dated the Closing Date,
executed on behalf of the Company by each of the President and Chief Executive Officer and the Chief Financial Officer of the Company, stating that: 

(i) The representations, warranties and agreements of the Company in Section 4.1 hereof are true and correct as of the Closing Date and
the Company has complied with all its agreements contained herein; 
 (ii) Such officers have carefully examined the Financial Statements
(as defined in Section 4.1(e) hereof) and, in their opinion, as of their respective dates (except to the extent superseded by statements in later-prepared documents comprising part of the Financial Statements), and as of the Closing Date, the
Financial Statements do not contain any untrue statement of a material fact nor omit to state any material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made,
not misleading; and 
 (iii) From the date of the Financial Statements to the Closing Date, there shall not have been any event or series
of events, change, occurrence or development or a state of circumstances or facts (including any events, changes, occurrences, developments, state of circumstances or facts existing prior to the date hereof but which become known during such period)
that, individually or in the aggregate, has had, or would reasonably be expected to have, a Material Adverse Effect (as defined in Section 4.1(g) hereof). 

(d) The Company shall have delivered a certificate of the Secretary of the Company, dated as of the Closing Date, (i) certifying the
resolutions adopted by the Board of Directors of the Company or a duly authorized committee thereof approving the transactions contemplated by this Agreement and the Registration Rights Agreement and the issuance of the Shares, (ii) certifying
the current versions of the certificate of incorporation, as amended, and bylaws of the Company and (iii) certifying as to the signatures and authority of persons signing this Agreement and related documents on behalf of the Company; 

(e) The Company shall have delivered a certificate evidencing the formation and good standing of each of the Company and Square 1 Bank in its
respective jurisdiction of formation issued by the Secretary of State (or comparable office) of such jurisdiction, as of a date within five (5) business days of the Closing Date; 

(f) Any authorizations, consents, commitments, agreements, orders or approvals or confirmation of non-objection of, or declarations,
notifications or filings with, or expirations of waiting periods imposed by, any federal, state or local court or governmental or regulatory agency or authority or applicable stock exchange or trading market, including the Board of Governors of the
Federal Reserve (the “Federal Reserve”), the Federal Deposit Insurance Corporation (the “FDIC”) and the North Carolina Commissioner of Banks (the “Commissioner”) (any such court, agency, authority,
exchange or market, including the Federal Reserve, a “Governmental Authority”) required for the consummation of the Transactions by the Company, as defined herein, shall have been obtained or filed or shall have occurred and any
such orders shall have become final, non-appealable orders, and there shall be no judgment, injunction, order or decree prohibiting any of the Transactions contemplated hereby, and no 

  
 3 

 
action, suit or proceeding shall be pending or threatened before or by any court or Governmental Authority seeking to restrain or prohibit, or seeking damages in connection with, the Transactions
contemplated hereby; 
 (g) Kilpatrick Townsend & Stockton LLP, counsel to the Company, shall have furnished to the Purchaser its
written opinion, addressed to the Purchasers and dated the Closing Date, substantially as set forth in Exhibit C hereto; 
 (h) The
Company shall have delivered to the Purchasers a schedule in the form of Schedule 3.1(h) attached hereto that identifies as of the time immediately after the Closing and assuming the sale of Shares as contemplated by this Agreement, the number of
shares and type of all authorized, issued and outstanding capital stock, options and other securities of the Company (whether or not then-presently convertible into or exercisable or exchangeable for shares of capital stock of the Company). 

(i) The Corporation shall have filed with the Secretary of State of the State of Delaware a Certificate of Amendment to the Certificate of
Designation, Rights and Preferences for the Class B Common Stock in the form attached hereto as Exhibit D. 
 3.2 Conditions to
the Company’s Obligations. 
 (a) The obligations of the Company hereunder are subject to the accuracy, as of the date hereof and
as of the Closing Date, of the representations and warranties of each Purchaser contained herein and to the performance by each Purchaser of its obligations hereunder. 

(b) Each Purchaser shall have received any and all necessary approvals or non-objections from all Governmental Authorities necessary for the
purchase by the Purchaser of the Shares pursuant to this Agreement, and any and all applicable waiting periods upon which such approvals are conditioned shall have expired. 
  

	 	4	REPRESENTATIONS AND WARRANTIES 

 4.1 Representations, Warranties and Agreements of the
Company. The Company represents and warrants to, and agrees with the Purchasers that as of the date hereof and immediately prior to the Closing: 

(a) The authorized capital stock of the Company consists of 45,000,000 shares of common stock, $0.01 par value and 10,000,000 shares of
preferred stock, $0.01 par value. As of the date of this Agreement, 18,117,664 shares of Class A Common Stock are outstanding, 1,976,313 shares of Class B Common Stock, par value $0.01 per share are outstanding, and 5,000 shares of Series A
Fixed Rate Cumulative Convertible Preferred Stock are outstanding. 
 (b) The Company and each Subsidiary (as defined below) have filed all
reports, registrations and statements, together with any required amendments thereto, that it was required to file with the Federal Reserve, the Securities and Exchange Commission (the “SEC”), the FDIC, the Commissioner and any
other applicable federal or state securities or banking authorities, except where the failure to file any such report, registration or statement would not 

  
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reasonably be expected to have a Material Adverse Effect (as defined below). All such reports and statements filed with any such regulatory body or authority are collectively referred to herein
as the “Company Reports.” As of their respective dates, the Company Reports complied as to form in all material respects with all the rules and regulations promulgated by the Federal Reserve, the FDIC, the Commissioner and any other
applicable foreign or state securities or banking authorities, as the case may be. For the purposes of this Agreement, the term “Subsidiary” shall mean any: (a) firm, Company, partnership, limited liability company, trust or
other entity of which the Company owns (i) at least 10% of the outstanding voting capital stock (or other outstanding voting shares of beneficial interest), or (ii) at least a majority of the partnership, membership, joint venture or
similar interests; (b) partnership in which the Company is a general partner; or (c) limited liability company in which the Company is the manager or the managing member. 

(c) Since December 31, 2011, no change has occurred and no circumstances exist (including any changes, occurrences, circumstances or
facts existing prior to December 31, 2011 but which became known on or after December 31, 2011) that is not disclosed in the Financial Statements (as defined below) which, individually or in the aggregate, have had or are reasonably likely
to have a Material Adverse Effect. There are no transactions, arrangements, or other relationships between the Company or any Subsidiary and an unconsolidated or other off balance sheet entity. Neither the Company nor any of its Subsidiaries is a
party to any material transaction or material contract or arrangement with any stockholder of the Company holding at least 10% of the outstanding shares of Common Stock (determined on a fully diluted basis), director, officer or employee of the
Company or any of its Subsidiaries (collectively, “Related Parties”) or any of the respective immediate family members or affiliates of Related Parties other than in the ordinary course of business. 

(d) The Company and each Subsidiary have all permits, licenses, authorizations, orders and approvals of, and have made all filings,
applications and registrations with, any governmental entities that are required in order to carry on their business as presently conducted and that are material to the business of the Company or such Subsidiary, except where the failure to have
such permits, licenses, authorizations, orders and approvals or the failure to make such filings, applications and registrations would not, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect; and all such
permits, licenses, certificates of authority, orders and approvals are in full force and effect and, to the knowledge of the Company, no suspension or cancellation of any of them is threatened, and all such filings, applications and registrations
are current. 
 (e) The Company has furnished to the Purchaser or otherwise made available a copy of the audited consolidated financial
statements of the Company for its fiscal years ended December 31, 2010 and 2011, and each interim period subsequent to the end of its fiscal year ended December 31, 2011 through June 30, 2012 (attached hereto as Schedule 4.1(e))
(collectively, the “Financial Statements”). The Financial Statements do not contain any untrue statement of material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading. 

  
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 (f) Based in part upon the representations and warranties of the Purchasers contained herein,
(i) the Company is not required by applicable law or regulation in connection with the offer, sale and delivery of the Shares to the Purchasers in the manner contemplated by this Agreement to register the Shares under the Securities Act, or any
state securities laws and (ii) none of the Company, its Subsidiaries nor, to the Company’s knowledge, any of its affiliates or any person acting on its behalf has, directly or indirectly, at any time within the past six months, made any
offers or sales of any Company security or solicited any offers to buy any security under circumstances that would (A) eliminate the availability of the exemption from registration under Regulation D under the Securities Act in connection
with the offer and sale by the Company of the Shares as contemplated hereby or (B) cause the offering of the Shares pursuant to this Agreement to be integrated with prior offerings by the Company for purposes of any applicable law, regulation
or stockholder approval provisions. Neither the Company nor any person acting on behalf of the Company has offered or sold any of the Shares by any form of general solicitation or general advertising. The Company has offered the Shares for sale only
to the Purchasers and certain other “accredited investors” within the meaning of Rule 501 under the Securities Act. 
 (g) The
Company and its Subsidiaries (i) have been duly incorporated or organized and are validly existing in good standing under the laws of their respective jurisdictions of incorporation or organization; (ii) are duly qualified to do business
and are in good standing as foreign corporations or organizations in each jurisdiction in which their respective ownership or lease of property or the conduct of their respective businesses requires such qualification, except where the failure to be
so qualified would not reasonably be expected to result in any material adverse change in the condition, financial or otherwise, or in the earnings, business affairs or business prospects of the Company and its Subsidiaries (taken as a whole), or
which would not reasonably be expected to materially and adversely affect the assets or properties of the Company and its Subsidiaries (taken as a whole), or which would not reasonably be expected to materially and adversely affect the Transactions
as defined herein (individually or in the aggregate, a “Material Adverse Effect”); and (iii) have all corporate power and authority necessary to own or hold their respective properties and to conduct the businesses in which
they are currently engaged. 
 (h) The number of shares and type of all authorized, issued and outstanding capital stock, options and other
securities of the Company (whether or not presently convertible into or exercisable or exchangeable for shares of capital stock of the Company) as of the date of this Agreement has been set forth on Schedule 4.1(h). All of the outstanding shares of
capital stock of the Company are duly authorized, validly issued, fully paid and non-assessable, have been issued in compliance in all material respects with all applicable federal and state securities laws. None of such outstanding shares was
issued in violation of any preemptive rights or similar rights to subscribe for or purchase any capital stock of the Company, and no person has any preemptive or similar right to purchase any shares of capital stock of the Company. Except as set
forth on Schedule 4.1(h), (i) there are no outstanding options, warrants, scrip, rights to subscribe to, calls or commitments of any character whatsoever relating to, or securities or rights convertible into, or exercisable or exchangeable for,
any shares of capital stock of the Company, or contracts, commitments, understandings or arrangements by which the Company is or may become bound to issue additional shares of capital stock of the Company or options, warrants, scrip, rights to
subscribe to, calls or commitments of any character whatsoever relating to, or 

  
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securities or rights convertible into, or exercisable or exchangeable for, any shares of capital stock of the Company, (ii) there are no outstanding securities or instruments of the Company
which contain any redemption or similar provisions, and there are no contracts, commitments, understandings or arrangements by which the Company is or may become bound to redeem a security of the Company; (iii) there are no securities or
instruments containing anti-dilution or similar provisions that will be triggered by the issuance of the Shares; (iv) the Company does not have any stock appreciation rights or “phantom stock” plans or agreements or any similar plan
or agreement; and (v) the Company has not exercised its right to defer payments of interest on the Fixed Rate Junior Subordinated Convertible Debt Securities due 2038 issued by Square 1 Financial Capital Trust 1 (the “Trust
Subsidiary”) pursuant to Section 2.11 of the Indenture dated September 30, 2008 between the Company and Wilmington Trust Company, a Delaware banking Company, as trustee of the Trust Subsidiary. 

(i) The Shares have been duly authorized and, when issued and delivered by the Company against payment therefor in the manner contemplated by
this Agreement, will be validly issued, fully paid and non-assessable, and, other than the preemptive rights provided in the First Amendment to the Stock Purchase Agreement by and between the Company and the Purchasers dated May 6, 2010 (the
“Purchaser Preemptive Rights”), there are no preemptive rights relating to the issuance of the Shares. 
 (j) Each of this
Agreement and the Registration Rights Agreement has been duly authorized, executed and delivered by the Company and constitutes a valid and legally binding agreement of the Company enforceable against the Company in accordance with its terms,
subject to the effects of bankruptcy, insolvency, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, and general equitable principles (whether considered in a proceeding in equity or at law).

 (k) The execution, delivery and performance of this Agreement, the issuance and sale of the Shares in the manner contemplated hereby, the
consummation of the transactions contemplated herein and the completion of the Private Placement (collectively, the “Transactions”), will not (i) conflict with or constitute a violation of, or default (with the passage of time
or the delivery of notice) under, (A) any bond, debenture, note or other evidence of indebtedness, or any agreement, lease, franchise, license, permit, contract, indenture, mortgage, deed of trust, loan agreement, joint venture or other
agreement or instrument to which the Company or any of its Subsidiaries is a party or by which it or any of its Subsidiaries or their property is bound, where such conflict, violation or default might reasonably be expected to have a Material
Adverse Effect, or (B) any law, administrative regulation, ordinance or judgment, order or decree of any court or governmental agency, arbitration panel or authority binding upon the Company or any of its Subsidiaries or any of their property,
where such conflict, violation or default might reasonably be expected to have a Material Adverse Effect, or (ii) violate any of the provisions of the Certificate of Incorporation, as amended, or Bylaws, as amended, of the Company; and no
consent, approval, authorization or order of, or filing or registration with any such person (including, without limitation, any such court or governmental agency or body) is required for the consummation of the Transactions by the Company, except
such as may be required under state securities laws or Regulation D under the Securities Act. 

  
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 (l) The Financial Statements (including the related notes) present fairly, in all material
respects, the financial condition and results of operations of the Company and Square 1 Bank, at the dates and for the periods indicated, and have been prepared in conformity with U.S. generally accepted accounting principles
(“GAAP”) applied on a consistent basis throughout the periods involved. 
 (m) There is no action, suit or proceeding
before or by any court or governmental agency or body or any labor dispute now pending or, to the knowledge of the Company, threatened against the Company or any of its Subsidiaries, which would reasonably be expected to have a Material Adverse
Effect. To the best knowledge of the Company, all pending legal, arbitral or governmental proceedings or investigations to which the Company or any of its Subsidiaries is a party or have been threatened, or of which any of their assets or properties
is the subject which are not described in the Financial Statements, including ordinary routine litigation incidental to the business of the Company or any of its Subsidiaries, is, considered in the aggregate, not material to the Company or any of
its Subsidiaries. 
 (n) No temporary restraining order, preliminary or permanent injunction or other order issued by any court of competent
jurisdiction or other legal restraint or prohibition preventing the consummation of the Transactions is in effect or, to the best knowledge of the Company, threatened. 

(o) Neither the Company nor any Subsidiary has engaged in conduct that it knew to be a violation of any applicable law or contractual
obligation relating to the recruitment, hiring, extension of offers of employment, retention or solicitation of any current employee of the Company or any Subsidiary. To the knowledge of the Company, no executive officer is, or is expected to be, in
violation of any material term of any employment contract, confidentiality, disclosure or proprietary information agreement or non-competition agreement, or any other contract or agreement or any restrictive covenant, and to the knowledge of the
Company, the continued employment of each such executive officer does not subject the Company or any of its Subsidiaries to any material liability with respect to any of the foregoing matters. 

(p) Except as set forth on Schedule 4.1(p), no broker’s, finder’s, investment banker’s or similar fee or commission has been
paid or will be payable by the Company with respect to, or for any services rendered to the Company ancillary to, the offer, issue and sale of the Shares contemplated by this Agreement. 

(q) The Company does not own or control, directly or indirectly, any Subsidiary other than Square 1 Bank, Square 1 Ventures, LLC and the
Trust Subsidiary. The Company does not engage in any business or activity other than investing its assets and owning or controlling Square 1 Bank, Square 1 Ventures LLC and the Trust Subsidiary. Except for short-term debt securities and shares
issued to the Company by the Trust Subsidiary and as set forth in Schedule 4.1(q), the Company does not own any shares of stock or any other equity or debt securities of any Company or other entity or have any equity interest in any firm,
partnership, limited liability company, joint venture, association or other entity except as set forth in the Financial Statements. 

  
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 (r) Except for such agreements that have expired or terminated in accordance with their terms
prior to the date hereof, each material agreement to which the Company and its Subsidiaries is a party, is in full force and effect and is binding on the Company and/or its Subsidiaries, as applicable, and, to the knowledge of the Company, is
binding upon such other parties, in each case in accordance with its terms, and neither the Company, any of its Subsidiaries nor, to the knowledge of the Company, any other party thereto, is in breach of or default under any such agreement, which
breach or default would reasonably be expected to have a Material Adverse Effect. Neither the Company, nor any of its Subsidiaries, has received any written notice regarding the termination of any such agreements. 

(s) Each of the Company and its Subsidiaries has filed on a timely basis all material federal, state, local and foreign income and franchise
tax returns required to be filed by it through the date hereof or had properly requested extension thereof and has paid all taxes shown as due thereon, and any related material assessments, fines or penalties. Each of the Company and its
Subsidiaries has made reasonably adequate charges, accruals and reserves in the applicable Financial Statements in respect of all federal, state, local and foreign income and franchise taxes for all periods as to which the tax liability of the
Company and its Subsidiaries has not been finally determined. The Company has no knowledge of a tax deficiency which has been or might be asserted or threatened against it or any of its Subsidiaries. 

(t) The Company and its Subsidiaries are in compliance in all material respects with all applicable laws, rules, regulations, orders, decrees
and judgments applicable to it, including, without limitation, all applicable local, state and federal environmental laws and the applicable federal and state banking laws, rules and regulations, (the “Applicable Laws”). Neither the
Company nor any of its Subsidiaries has received any notice of purported or actual non-compliance with Applicable Laws. Neither the Company nor any of its Subsidiaries has received any communication from any Governmental Authority
(i) threatening to revoke any permit, license, franchise, certificate of authority or other governmental authorization, or (ii) threatening or contemplating revocation or limitation of, or which would have the effect of revoking or
limiting, FDIC deposit insurance. 
 (u) The operations of the Company and its Subsidiaries are and have been conducted, in all material
respects, in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations
thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Money Laundering Laws”) and no action, suit or proceeding by or before any court
or governmental agency, authority or body or any arbitrator involving the Company or any of its Subsidiaries with respect to the Money Laundering Laws is pending or, to the knowledge of the Company, threatened. 

(v) Neither the Company nor any of its Subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or affiliate
of the Company or any of its Subsidiaries, is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Treasury Department (“OFAC”). 

  
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 (w) Each of the Company and its Subsidiaries has good and marketable title to all properties and
assets reflected as owned by it in the Financial Statements and that it otherwise purports to own, and such properties and assets are not subject to any lien, mortgage, pledge, or security interest except (i) those, if any, securing debt
reflected in the Financial Statements, or (ii) those which are not material in amount or do not adversely affect the use made and intended to be made of such property by the Company or its Subsidiaries. Each of the Company and its Subsidiaries
holds its leased properties under valid and binding leases, with such exceptions as would not reasonably be expected to have a Material Adverse Effect. Except as disclosed in the Financial Statements, each of the Company and its Subsidiaries owns or
leases all such properties as are necessary to its operations as now conducted. 
 (x) Each of the Company and its Subsidiaries maintains
insurance (issued by insurers of recognized financial responsibility) of the types, against such losses and in the amounts, with such insurers and subject to deductibles and exclusions as the Company reasonably believes are customary in the
Company’s and its Subsidiaries’ industry and otherwise reasonably prudent, including, without limitation, insurance covering all real and personal property owned or leased by the Company and its Subsidiaries against theft, damage,
destruction, acts of vandalism and all other risks customarily insured against by similarly situated companies, all of which insurance is in full force and effect and no written notice of cancellation has been received. 

(y) The Company is not and, after giving effect to the offering and sale of the Shares as contemplated in this Agreement will not be, an
“investment company” as defined in the Investment Company Act of 1940, as amended. 
 (z) The Company is duly registered as a bank
holding company under the Bank Holding Company Act of 1956, as amended. Square 1 Bank is a commercial bank duly organized, validly existing and in good standing with the Commissioner. Square 1 Bank has at least a “satisfactory” rating
under the U.S. Community Reinvestment Act. Square 1 Bank is a member in good standing of the Federal Home Loan Bank of Atlanta. Square 1 Bank’s deposit accounts are insured up to applicable limits by the FDIC, and all premiums and assessments
required to be paid in connection therewith have been paid when due. Square 1 Bank meets or exceeds the standards necessary to be considered “well capitalized” under the FDIC’s regulatory framework for prompt corrective action. 

(aa) Neither the Company nor any Subsidiary is subject to any cease-and-desist or other similar order or enforcement action (including any
order to pay civil money penalties) issued by, or is a party to any written agreement, consent agreement or memorandum of understanding with, or is a party to any commitment letter or similar undertaking to, or is subject to any capital directive
by, or since December 31, 2011, has adopted any board resolutions at the request of, any governmental entity that currently restricts in any material respect the conduct of its operations or business or that in any material manner relates to
its capital adequacy, maintenance of specific capital levels, its liquidity and funding policies and practices, its ability to pay dividends, its credit, risk management or compliance policies, its internal controls, its management or its operations
or business (each item in this sentence, a “Regulatory Agreement”), nor has the Company or any Subsidiary been advised since December 31, 2011 by any Governmental Authority that it is considering issuing, initiating, ordering,
or requesting any such Regulatory Agreement. 

  
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 (bb) The Company is not, and has never been, an issuer identified in Rule 144(i)(1) under the
Securities Act. 
 (cc) As of the Closing Date, except for normal periodic examinations conducted or being conducted by a federal or state
bank regulatory authority having jurisdiction over the Company or any of its Subsidiaries (a “Bank Regulator”), since December 31, 2011, no Bank Regulator has initiated any proceeding or, to the best knowledge of the Company,
investigation into the business or operations of the Company or any of its Subsidiaries. The Company and its Subsidiaries have addressed in all material respects any matters requiring Board attention set forth in writing by any Bank Regulator with
respect to any such normal periodic examination. 
 (dd) At the Closing Date, taking into account the proceeds of the capital raise
contemplated as part of this Transaction, the Company, on a consolidated basis, and the Company’s bank Subsidiary will each have a leverage ratio of not less than 8.0% and a total risk-based capital ratio of not less than 12.0%. 

(ee) As of the date hereof and as of the Closing Date, the Company’s management has concluded that the loan loss reserves of the
Company’s bank Subsidiary are adequate. 
 (ff) The issuance of the Shares to the Purchasers as contemplated by this Agreement will not
trigger any rights under any “change of control” provision in any of the agreements to which the Company or any of its Subsidiaries is a party, including any employment, “change in control,” severance or other compensatory
agreements and any benefit plan, which results in payments to the counterparty or the acceleration of vesting of benefits. 
 (gg) The
Company represents and warrants that the Company has not entered into any side letter or letter agreement or any similar agreement with any of the parties to this Agreement (a “Side Letter”) that has the effect of establishing rights or
otherwise benefiting any party to this Agreement in a manner more favorable in any material respect to such party than the rights and benefits established in favor of the other Purchasers under this Agreement. 

4.2 Representations and Warranties and Agreements of the Purchaser. Each Purchaser represents and warrants to, and agrees with, the
Company that, as of the date hereof and immediately prior to the Closing: 
 (a) The Purchaser has full power and authority to enter into
this Agreement and this Agreement constitutes a valid and legally binding obligation of the Purchaser, enforceable against the Purchaser in accordance with its terms, subject to the effects of bankruptcy, insolvency, reorganization, moratorium and
other similar laws relating to or affecting creditor’s rights generally, and general equitable principles (whether considered in a proceeding in equity or at law). 

  
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 (b) The Purchaser is duly organized, validly existing and in good standing in the jurisdiction of
its incorporation and has all the requisite power and authority to purchase the Shares, as provided herein, and (ii) such investment has been duly authorized by all necessary action on behalf of the Purchaser. 

(c) The Purchaser is purchasing the Shares for the Purchaser’s own account and not with a view to or for sale in connection with any
distribution thereof in a transaction that would violate or cause a violation of the Securities Act or the securities laws of any state or any other applicable jurisdiction. The Purchaser has not been organized solely for the purpose of acquiring
the Shares. 
 (d) The Purchaser is an “accredited investor” as defined in Rule 501(a) promulgated under the Securities Act and
understands and agrees that the offer and sale of the Shares to the Purchaser pursuant to this Agreement have not been registered under the Securities Act or any state securities law in reliance on the availability of an exemption from such
registration requirements of the Securities Act based on the accuracy of the Purchaser’s representations in this Section 4.2. 

(e) In the normal course of the Purchaser’s business or affairs, the Purchaser invests in or purchases securities similar to the Shares
and has such knowledge and experience in financial and business matters as to be capable of evaluating the merits and risks of purchasing the Shares. The Purchaser has received and has carefully reviewed the Financial Statements. The Purchaser has
had access to such financial and other information concerning the Company and Square 1 Bank as Purchaser deemed necessary or desirable in making a decision to purchase the Shares, including an opportunity to ask questions and receive answers from
officers of the Company and to obtain additional information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify the accuracy of any information furnished to the
Purchaser or to which the Purchaser had access. 
 (f) The Purchaser is not relying on the Company or any of its affiliates with respect to
an analysis or consideration of the terms of or economic considerations relating to an investment in the Shares. In regard to such considerations and analysis, the Purchaser has relied on the advice of, or has consulted with its own advisors, other
than those advisors of the undersigned affiliated with the Company or any of its affiliates. 
 (g) The Purchaser acknowledges and is aware
that there are substantial restrictions on the transferability of the Shares. The Purchaser understands that the Shares have not been registered under the Securities Act and are “restricted securities” within the meaning of Rule 144 of the
Securities Act, and may not be sold, transferred, or otherwise disposed of without registration under the Securities Act or an exemption therefrom. Furthermore, the Purchaser acknowledges that the Shares purchased hereunder will bear a legend to the
effect set forth below, and the Purchaser covenants that, except to the extent such restrictions are waived by the Company, the Purchaser shall not transfer the Shares without complying with the restrictions on transfer described in the legend
endorsed on such certificate: 
 THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE 

  
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SOLD, TRANSFERRED, ASSIGNED, PLEDGED, OR HYPOTHECATED ABSENT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR COMPLIANCE WITH RULE 144 PROMULGATED UNDER SUCH ACT, OR UNLESS THE COMPANY HAS
RECEIVED AN OPINION OF COUNSEL, REASONABLY SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED. 
 The
restrictive legend set forth in this Section 4.2(g) shall be removed and the Company shall issue a certificate without such restrictive legend or any other restrictive legend to the holder of the applicable Shares upon which it is stamped or
issue to such holder by electronic delivery at the applicable balance account at the Depository Trust Company (“DTC”), if (i) such Shares are registered for resale under the Securities Act, (ii) such Shares are sold or
transferred pursuant to Rule 144, or (iii) such Shares are eligible for sale under Rule 144, without the requirement for the Company to be in compliance with the current public information required under Rule 144 as to such securities and
without volume or manner-of-sale restrictions. Following the earlier of (i) the effective date of the first Registration Statement covering the resale of some or all of the Shares (the “Effective Date”) or (ii) Rule 144
becoming available for the resale of Shares, without the requirement for the Company to be in compliance with the current public information required under Rule 144 as to the Shares and without volume or manner-of-sale restrictions, the Company
shall cause counsel to the Company to issue to the Company’s transfer agent a legal opinion to the effect that no subsequent transfer of such Shares shall require registration under the Securities Act. Any fees (with respect to said transfer
agent, counsel or otherwise) associated with the issuance of such opinion or the removal of such legend shall be borne by the Company. Following such time as a restrictive legend is no longer required for certain Shares, the Company will no later
than 3 trading days following the delivery by the Purchaser to the Company or said transfer agent (with notice to the Company) of a legended certificate representing such Shares and an opinion of counsel to the extent required by this
Section 4.2(g) deliver or cause to be delivered to the Purchaser a certificate representing such Shares that is free from all restrictive legends. Unless otherwise required by applicable law, the Company may not make any notation on its records
or give instructions to the transfer agent that enlarge the restrictions on transfer set forth in this Section 4.2(g). Certificates for Shares free from all restrictive legends may be transmitted by the said transfer agent to the Purchaser by
crediting the account of the Purchaser’s custodian or prime broker with DTC as directed by the Purchaser. 
  

	 	5	ADDITIONAL AGREEMENTS 

 5.1 Form D and Blue Sky. The Company agrees to file a Form D with
respect to the Shares as required under Regulation D and to provide a copy thereof to the Purchasers promptly after such filing. The Company, on or before the Closing Date, shall take such action as the Company shall reasonably determine is
necessary in order to obtain an exemption for or to qualify the Shares for sale to the Purchasers at the Closing pursuant to this Agreement under applicable securities or “Blue Sky” laws of the states of the United States (or to
obtain an exemption from such qualification), and shall provide evidence of any such action so taken to the Purchasers on or prior to the Closing Date. The Company shall make all filings and reports relating to the offer and sale of the Securities
required under applicable securities or “Blue Sky” laws of the states of the United States following the Closing Date. 

  
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 5.2 Regulatory Matters. Each of the Company and each Purchaser agrees to use its
reasonable best efforts to take all actions and to do all things necessary, proper or advisable to obtain any authorizations, consents, orders, approvals and/or non-objections of all Governmental Authorities necessary for the Purchaser to purchase
the Shares on the Closing Date on terms consistent with the terms set forth in this Agreement. 
 5.3 Confidentiality. 

(a) For so long as a Purchaser owns any Shares, the Purchaser agrees and agrees to cause its Representatives (as defined in
Section 5.3(c) below) (to the extent such Representatives are provided any such Confidential Information (as defined in Section 5.3(b) below) by the Company or the Purchaser), to keep confidential any Confidential Information. In the event
the Purchaser pursuant to this Agreement or anyone to whom it transmits Confidential Information is requested or required by oral questions, interrogatories, requests for information or documents, subpoenas, civil investigative demand or similar
process to disclose any such information, the Purchaser shall (i) provide the Company with prompt notice so that the Company may seek a protective order or other appropriate remedy and/or waive the Purchaser’s compliance with the
provisions of this section, (ii) furnish only that portion of such information that the Purchaser is advised by counsel is responsive to the request or legally required and (iii) at the Company’s expense and direction, exercise its
reasonable efforts to obtain reliable assurance that confidential treatment will be accorded such information. Notwithstanding the foregoing, the Purchaser may disclose any such information if required by judicial or administrative process or by
other requirements of law, national stock exchange or self-regulatory organization. 
 (b) For the purpose of this Agreement,
“Confidential Information” means information obtained from the Company, except to the extent that such information can be shown to have been (i) previously known on a non-confidential basis by the Purchaser or its
Representatives, (ii) in the public domain other than by breach of this Agreement by the Purchaser or its Representatives or (iii) later acquired by the Purchaser from sources other than the Company or Square 1 Bank not known by the
Purchaser or its Representatives, as applicable, to be bound by any confidentiality obligation to the Company or Square 1 Bank with respect to such information. 

(c) For purposes of this Agreement, “Representative” shall mean, with respect to any person, any of such person’s
officers, directors, employees, agents, attorneys, accountants, consultants, equity financing partners, general partners, managers, investment managers, or financial advisors or other person associated with, or acting for or on behalf of, such
person. 
 5.4 Subsequent Sales of Common Stock. Other than the approval of the holder of the outstanding shares of Class B Common
Stock to increase the number of authorized shares of Class B Common Stock, the Company shall not take any action or omit to take any action which would cause the Transactions or any portion thereof to require a vote of the Company’s
stockholders. 

  
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 5.5 No Change of Control. The Company shall use reasonable best efforts to obtain all
necessary irrevocable waivers, adopt any required amendments and make all appropriate determinations so that the issuance of the Shares to the Purchasers, either individually or in connection with the Shares sold in the Private Placement, will not
trigger a “change of control” or other similar provision in any of the agreements to which the Company or any of its Subsidiaries is a party, including without limitation any employment, “change in control,” severance or other
agreements and any benefit plan, which results in payments to the counterparty or the acceleration of vesting of benefits. 
 5.6 No
Additional Issuances. Between the date of this Agreement and the Closing Date, except for the issuance of shares of Common Stock issuable as of the date hereof as set forth in Schedule 4.1(h) and the issuance of the Shares contemplated by this
Agreement, the Company shall not issue any additional shares of Common Stock or other securities which provide the holder thereof the right to convert such securities into shares of Common Stock. 

5.7 Governance Matters. 

(a) On or after the Closing Date and so long as the Endicott Funds beneficially own shares of Common Stock equal in the aggregate to at least
4.9% of the outstanding shares of Common Stock (as adjusted from time to time for any reorganization, recapitalization, reclassification, stock dividend, stock split, reverse stock split, or other like changes in the Company’s capitalization),
upon Endicott’s written request the Company will cause one person nominated by Endicott and mutually agreeable to the Company and Endicott to be elected or appointed to the Board of Directors (the “Board Representative”), subject to
satisfaction of all legal and governance requirements regarding service as a director of the Company and to the reasonable approval of the Company’s Board of Directors or the appropriate committee thereof. After such appointment for election,
so long as the Endicott Funds beneficially own shares of Common Stock equal in the aggregate to at least 4.9% of the outstanding shares of Common Stock (as adjusted from time to time for any reorganization, recapitalization, reclassification, stock
dividend, stock split, reverse stock split, or other like changes in the Company’s capitalization), the Company will be required to recommend to its stockholders the election of the Board Representative at the Company’s annual meeting at
which such Board Representative’s term expires, subject to satisfaction of all legal and governance requirements regarding service as a director of the Company and to the reasonable approval of the Company’s Board of Directors or the
appropriate committee thereof, to the Board of Directors. If the Endicott Funds no longer hold in the aggregate the minimum number of shares of Common Stock specified in the prior sentence, Endicott will have no further rights under Sections 5.7
(a) through 5.7 (c) and, at the written request of the Company’s Board of Directors, shall use all reasonable best efforts to cause the Board Representative to resign from the Board of Directors as promptly as possible thereafter.

 (b) The Board Representative (including any successor nominee mutually agreeable to the Company and Endicott) duly selected in accordance
with Section 5.7 (a) shall, subject to applicable law, be the Company’s and the Board of Directors’ nominee to serve on the Board of Directors of the Company. The Company shall use all reasonable best efforts to have the Board
Representative elected as a director of the Company and the Company shall solicit proxies for each such person to the same extent as it does for any of its other nominees to the Board of Directors. 

  
 15 

 (c) Subject to continued compliance with the ownership requirements of Section 5.7 (a),
Endicott shall have the power to designate the Board Representative’s replacement (who shall be mutually agreeable to the Company and Endicott) upon the death, resignation, retirement, disqualification or removal from office of such director,
subject to satisfaction of all legal and governance requirements regarding service as a director of the Company and to the reasonable approval of the Board of Directors or the appropriate committee thereof (such approval not to be unreasonably
withheld or delayed). The Board of Directors will promptly take all action reasonably required to fill the vacancy resulting therefrom with such person (including such person, subject to applicable law, being the Company’s and the Board of
Directors’ nominee to serve on the Board of Directors, using best efforts to have such person elected as director of the Company, and soliciting proxies for such person, to the same extent as it does for any of its other nominees to the Board
of Directors). 
 (d) The Board Representative shall be entitled to the same compensation and same indemnification in connection with his or
her role as a director as the other members of the Board of Directors, and each Board Representative shall be entitled to reimbursement for documented, reasonable out-of-pocket expenses incurred in attending meetings of the Board of Directors or any
committees thereof, to the same extent as the other members of the Board of Directors. The Company shall notify each Board Representative of all regular and special meetings of the Board of Directors and shall notify each Board Representative of all
regular and special meetings of any committee of the Board of Directors of which the Board Representative is a member in accordance with the Company’s Bylaws as then in effect. The Company shall provide each Board Representative with copies of
all notices, minutes, consents and other materials provided to all other members of the Board of Directors concurrently as such materials are provided to the other members. 

(e) The Board Representative shall have the right to attend regular and special meetings of the board of directors of Square 1 Bank; however,
such Board Representative shall have no right to vote and shall not attend sessions of the Board during which there is being discussed (i) matters involving this Agreement, (ii) information or material that Square 1 Bank is required or
obligated to maintain as confidential under applicable laws or regulations or policies or procedures of Square 1 Bank, or (iii) pending or threatened litigation or investigations if, in the opinion of counsel to Square 1 Bank, the presence of
such designee would or might adversely affect the confidential nature of or any privilege relating to the matters being discussed. 
 (f) In
order to facilitate the continuing interaction of Endicott with the Company, and in order to keep Endicott fully advised of all ongoing activities of the Company and Square 1 Bank, subject to the limitations in this Section, the Company agrees to
allow Robert I. Usdan and/or Steven Didion to attend as an invited guest and fully monitor all called meetings of the board of directors of the Company and Square 1 Bank . The Company and Square 1 Bank shall promptly give Endicott prior notice by
telephone of all called meetings. Any such representative shall only be permitted to observe at the meetings, and shall have no right to vote and may be excluded from sessions of the boards of directors during which there is being discussed
(i) matters involving this Agreement, (ii) information or material that the 

  
 16 

 
Company or Square 1 Bank are required or obligated to maintain as confidential under applicable laws or regulations or policies or procedures of the Company or Square 1 Bank, or
(iii) pending or threatened litigation or investigations if, in the opinion of counsel to the Company or Square 1 Bank, the presence of such designee would or might adversely affect the confidential nature of or any privilege relating to the
matters being discussed. 
 (g) Endicott and the Company acknowledge that this Section 5.7 supersedes and replaces Section 5.11 of
the Stock Purchase Agreement, dated April 28, 2010 and as amended, between the Company and Endicott. 
 5.8 Waiver of Preemptive/Pro
Rata Participation Rights 
 All preemptive rights and pro rata participation rights granted to the Purchasers under
Section 5.14(a) of the Stock Purchase Agreement in connection with the May 21, 2010 private placement offering of Company capital stock are hereby waived by each Purchaser insofar as they relate to the issuance and the sale of the
Class A Common Stock and Class B Common Stock in the Participation Offering and the issuance and the sale of the Class A Common Stock in the Additional Offering. 

5.9 Indemnification of Purchasers. The Company shall indemnify and hold the Purchasers harmless from and against all claims in respect
of all fees paid to Sandler O’Neill in connection with this Agreement and the Private Placement. 
  

	 	6	TERMINATION 

 6.1 Procedure for Termination. 

This Agreement may be terminated with respect to a Purchaser, and the Transactions contemplated hereby abandoned with respect to such
Purchaser, at any time prior to the Closing Date without liability, including for damages and out-of-pocket expenses: 
 (a) by the mutual
written consent of the Purchaser and the Company; 
 (b) by either the Purchaser or the Company if either (i) any approval, consent or
waiver of a Governmental Authority required to permit consummation of the Transactions contemplated by this Agreement shall have been denied or (ii) any Governmental Authority of competent jurisdiction shall have issued an order enjoining or
otherwise prohibiting consummation of the transactions contemplated by this Agreement; or 
 (c) by either the Purchaser or the Company if
the Closing has not occurred on or before September 30, 2012. 
  

	 	7	MISCELLANEOUS 

 7.1 Survival of Representations and Warranties. All statements contained
in any officers’ certificates delivered by or on behalf of the Company or Square 1 Bank pursuant to this Agreement or in connection with the Transactions will be deemed representations or warranties of the Company under this Agreement. All
representations and warranties contained in this 

  
 17 

 
Agreement made by or on behalf of the Company or the Purchaser will survive the execution and delivery of this Agreement, any investigation at any time made by or on behalf of the Company or the
Purchaser, and the sale and purchase of the Shares under this Agreement, and shall expire on the 12th month anniversary of the Closing Date. 

7.2 Successors and Assigns. This Agreement shall be binding upon and inure to the benefit of and be enforceable by or against the
respective successors and assigns of the parties hereto. This Agreement may not be assigned by the Company or any Purchaser without the prior written consent of the other party hereto; provided that a Purchaser may assign the Agreement to any
of its affiliates who execute an instrument in writing agreeing to be bound by the terms of this Agreement, which assignment shall not relieve the Purchaser of its obligations hereunder. 

7.3 Indemnification. 

(a) In consideration of the Purchaser’s execution and delivery of this Agreement and acquiring the Shares thereunder and in addition to
all of the Company’s other obligations under this Agreement, the Company shall defend, protect, indemnify and hold harmless the Purchaser and each other holder of the Shares and all of their stockholders, partners, members, officers, directors,
employees and direct or indirect investors and any of the foregoing persons’ agents or other representatives (including, without limitation, those retained in connection with the Transactions) (collectively, the “Indemnitees”) from
and against any and all actions, causes of action, suits, claims, losses, costs, penalties, fees, liabilities and damages, and expenses in connection therewith (irrespective of whether any such Indemnitee is a party to the action for which
indemnification hereunder is sought), and including reasonable attorneys’ fees and disbursements (the “Indemnified Liabilities”), incurred by any Indemnitee as a result of, or arising out of, or relating to (a) any
misrepresentation or breach of any representation or warranty made by the Company in this Agreement or any other certificate, instrument or document contemplated hereby or thereby, (b) any breach of any covenant, agreement or obligation of the
Company contained in this Agreement or any other certificate, instrument or document contemplated hereby or thereby, or (c) any cause of action, suit or claim brought or made against such Indemnitee by a third party (including for these
purposes a derivative action brought on behalf of the Company) and arising out of or resulting from (i) the execution, delivery, performance or enforcement of this Agreement or any other certificate, instrument or document contemplated hereby
or thereby, or (ii) any transaction financed or to be financed in whole or in part, directly or indirectly, with the proceeds of the issuance of the Shares. To the extent that the foregoing undertaking by the Company may be unenforceable for
any reason, the Company shall make the maximum contribution to the payment and satisfaction of each of the Indemnified Liabilities which is permissible under applicable law. 

(b) Promptly after receipt by an Indemnitee under this Section 7.3 of notice of the commencement of any action or proceeding (including
any governmental action or proceeding) involving an Indemnified Liability, such Indemnitee shall, if a claim for indemnification in respect thereof is to be made against any indemnifying party under this Section 7.3, deliver to the indemnifying
party a written notice of the commencement thereof, and the indemnifying party shall have the right to participate in, and, to the extent the indemnifying party so desires, jointly with any other indemnifying party similarly noticed, to assume
control of the defense thereof with counsel mutually satisfactory to the indemnifying party and the 

  
 18 

 
Indemnitee; provided, however, that an Indemnitee shall have the right to retain its own counsel with the fees and expenses of not more than one counsel for such Indemnitee to be paid by the
indemnifying party, if, in the reasonable opinion of the Indemnitee, the representation by such counsel of the Indemnitee and the indemnifying party would be inappropriate due to actual or potential differing interests between such Indemnitee and
any other party represented by such counsel in such proceeding. The Indemnitee shall cooperate fully with the indemnifying party in connection with any negotiation or defense of any such action or Indemnified Liabilities by the indemnifying party
and shall furnish to the indemnifying party all information reasonably available to the Indemnitee that relates to such action or Indemnified Liabilities. The indemnifying party shall keep the Indemnitee fully apprised at all times as to the status
of the defense or any settlement negotiations with respect thereto. No indemnifying party shall be liable for any settlement of any action, claim or proceeding effected without its prior written consent, provided, however, that the indemnifying
party shall not unreasonably withhold, delay or condition its consent. No indemnifying party shall, without the prior written consent of the Indemnitee, which consent shall not be unreasonably withheld conditioned or delayed, consent to entry of any
judgment or enter into any settlement or other compromise which (i) does not include as an unconditional term thereof the giving by the claimant or plaintiff to such Indemnitee of a release from all liability in respect to such Indemnified
Liabilities or litigation, (ii) requires any admission of wrongdoing by such Indemnitee, or (iii) obligates or requires an Indemnitee to take, or refrain from taking, any action. Following indemnification as provided for hereunder, the
indemnifying party shall be subrogated to all rights of the Indemnitee with respect to all third parties, firms or corporations relating to the matter for which indemnification has been made. The failure to deliver written notice to the indemnifying
party within a reasonable time of the commencement of any such action shall not relieve such indemnifying party of any liability to the Indemnitee under this Section 7.3, except to the extent that the indemnifying party is prejudiced in its
ability to defend such action. 
 (c) The indemnification required by this Section 7.3 shall be made by periodic payments of the amount
thereof during the course of the investigation or defense, as and when bills are received or Indemnified Liabilities are incurred. 
 7.4
No Strict Construction. The language used in this Agreement will be deemed to be the language chosen by the parties to express their mutual intent, and no rules of strict construction will be applied against any party. 

7.5 Payment Set Aside. To the extent that the Company makes a payment or payments to the Purchaser hereunder or the Purchaser enforces
or exercises its rights hereunder, and such payment or payments or the proceeds of such enforcement or exercise or any part thereof are subsequently invalidated, declared to be fraudulent or preferential, set aside, recovered from, disgorged by or
are required to be refunded, repaid or otherwise restored to the Company, a trustee, receiver or any other person under any law (including, without limitation, any bankruptcy law, foreign, state or federal law, common law or equitable cause of
action), then to the extent of any such restoration the obligation or part thereof originally intended to be satisfied shall be revived and continued in full force and effect as if such payment had not been made or such enforcement or setoff had not
occurred. 

  
 19 

 7.6 Corporate Opportunities. Each of the parties hereto acknowledges that the Purchaser
and its affiliates and related investment funds may review the business plans and related proprietary information of any enterprise, including enterprises which may have products or services which compete directly or indirectly with those of the
Company and its subsidiaries, and may trade in the securities of such enterprise. Neither Purchaser nor any of its affiliates or related investment funds shall be precluded or in any way restricted from investing or participating in any particular
enterprise, or trading in the securities thereof whether or not such enterprise has products or services that compete with those of the Company and its subsidiaries. The parties expressly acknowledge and agree that: (a) Purchaser or its
affiliates have the right to, and shall have no duty (contractual or otherwise) not to, directly or indirectly, engage in the same or similar business activities or lines of business as the Company and its Subsidiaries; and (b) in the event
that Purchaser or its affiliates acquires knowledge of a potential transaction or matter that may be a corporate opportunity for the Company or any of its subsidiaries, Purchaser or its affiliates shall have no duty (contractual or otherwise) to
communicate or present such corporate opportunity to the Company or any of its subsidiaries, and, notwithstanding any provision of this Agreement to the contrary, shall not be liable to the Company or any of its subsidiaries or any other Purchasers
or shareholders of the Company for breach of any duty (contractual or otherwise) by reason of the fact that Purchaser, any affiliate thereof or related investment fund thereof, directly or indirectly, pursues or acquires such opportunity for itself,
directs such opportunity to another person, or does not present such opportunity to the Company or its subsidiaries. Notwithstanding the foregoing, a Board Representative of Purchaser shall be subject to, and comply with, the Company’s Code of
Ethics for Directors, including the provisions therein relating to conflicts of interest; provided, however, that if a Board Representative acquires knowledge of a potential transaction or matter that may be a corporate opportunity for the Company
or any of its Subsidiaries, such opportunity shall belong to the Company unless such corporate opportunity is, in the first instance, expressly offered to such person solely in his or her capacity with a Purchaser or its affiliates, in which case
such corporate opportunity shall belong to such Purchaser and its affiliates. 
 7.7 Reservation of Class A Common Stock. The
Company shall reserve, and will continue to reserve, free of any preemptive or similar rights of shareholders of the Company, a number of unissued shares of Class A Common Stock to which Purchaser’s shares of Class B Common Stock are
convertible. 
 7.8. Notices. All written communications provided for herein are required to be sent by U.S. Certified Mail or
recognized overnight delivery service (with charges prepaid) as follows: 
 (i) if to a Purchaser: 

To the address set forth on Exhibit A next to such Purchaser’s name 

  
 20 

 and (ii) if to the Company, addressed to it at: 

Square 1 Financial Inc. 
 406
Blackwell Street, Suite 240 
 Durham, North Carolina 27701 

Attention: Beth Reeves, Corporate Secretary 
 or
at such other address as the Company may have specified to the Purchaser in writing. All such notices shall be deemed received on the date of receipt by the recipient thereof if received prior to 5:00 p.m. on a business day in the place of receipt.
Otherwise, any such notice shall be deemed to have been received on the next succeeding business day in the place of receipt. 
 7.9.
Governing Law; Jurisdiction; Jury Trial. All questions concerning the construction, validity, enforcement and interpretation of this Agreement shall be governed by the internal laws of the State of Delaware, without giving effect to any
choice of law or conflict of law provision or rule (whether of the State of Delaware or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of Delaware. Each party hereby irrevocably
submits to the exclusive jurisdiction of the state and federal courts sitting in the City of Wilmington, Delaware for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or discussed
herein, and hereby irrevocably waives, and agrees not to assert in any suit, action or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action or proceeding is brought in an inconvenient
forum or that the venue of such suit, action or proceeding is improper. Each party hereby irrevocably waives personal service of process and consents to process being served in any such suit, action or proceeding by mailing a copy thereof to such
party at the address for such notices to it under this Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof. Nothing contained herein shall be deemed to limit in any way any right to serve
process in any manner permitted by law. EACH PARTY HEREBY IRREVOCABLY WAIVES ANY RIGHT IT MAY HAVE, AND AGREES NOT TO REQUEST, A JURY TRIAL FOR THE ADJUDICATION OF ANY DISPUTE HEREUNDER OR IN CONNECTION WITH OR ARISING OUT OF THIS AGREEMENT OR ANY
TRANSACTION CONTEMPLATED HEREBY. 
 7.10. Counterparts. This Agreement may be executed in one or more counterparts and, if executed
in more than one counterpart, the executed counterparts shall each be deemed to be an original, but all such counterparts shall together constitute one and the same instrument. 

7.11. Headings. The headings herein are inserted for convenience of reference only and are not intended to be part of, or to affect the
meaning or interpretation of, this Agreement. 
 7.12. Severability. Any provision of this Agreement that is prohibited or
unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof, and any such prohibition or unenforceability in any
jurisdiction shall (to the full extent permitted by law) not invalidate or render unenforceable such provision in any other jurisdiction. 

  
 21 

 7.13. Expenses. Each of the Company and the Purchasers shall be solely responsible for any
expenses or costs that such party may have incurred in connection with this Agreement and the Transactions. 
 7.14. Construction.
Each agreement contained herein shall be construed (absent express provision to the contrary) as being independent of each other agreement contained herein, so that compliance with any one agreement shall not (absent such an express contrary
provision) be deemed to excuse compliance with any other agreement. Where any provision herein refers to action to be taken by any person or entity, or which such person or entity is prohibited from taking, such provision shall be applicable whether
such action is taken directly or indirectly by such person or entity. 
 7.15. Entire Agreement; Amendments. This Agreement
supersedes all other prior oral or written agreements between the Purchaser, the Company, their affiliates and persons acting on their behalf with respect to the matters discussed herein, and this Agreement and the instruments referenced herein,
including the Registration Rights Agreement, contain the entire understanding of the parties with respect to the matters covered herein and therein and, except as specifically set forth herein or therein, neither the Company nor the Purchaser makes
any representation, warranty, covenant or undertaking with respect to such matters; provided, however, that the Stock Purchase Agreement, as amended, and Tag Along Rights Agreement, each entered into by and between each Purchaser and
the Company in connection with the Company’s May 21, 2010 private placement offering, shall not be and is not superceded by this Agreement. No provision of this Agreement may be amended other than by an instrument in writing signed by each
of the parties hereto. No provision hereof may be waived other than by an instrument in writing signed by the party against whom enforcement is sought. The Company has not, directly or indirectly, made any agreements with any Purchasers relating to
the terms or conditions of the Transactions except as set forth herein and the Registration Rights Agreement. Without limiting the foregoing, the Company confirms that, except as set forth in this Agreement, the Purchaser has not made any commitment
or promise or has any other obligation to provide any financing to the Company or otherwise. 
 7.16. No Third Party Beneficiaries.
This Agreement is intended for the benefit of the parties hereto and their respective permitted successors and assigns, and is not for the benefit of, nor may any provision hereof be enforced by, any other person other than Indemnities. 

[SIGNATURE PAGE FOLLOWS] 

  
 22 

 If the foregoing correctly sets forth the agreement between the Company and the Purchaser, please
indicate your acceptance in the space provided for that purpose below. 
  

					
	Very truly yours,
	
	SQUARE 1 FINANCIAL, INC.
		
	By:	 	 /s/ Douglas H. Bowers

		 	Name:	 	Douglas Bowers
		 	Title:	 	President and Chief Executive Officer
		
	By:	 	 /s/ John Pietrzak

		 	Name:	 	John Pietrzak
		 	Title:	 	Principal
		
		 	Castle Creek Capital Partners IV, L.P.

 If the foregoing correctly sets forth the agreement between the Company and the Purchaser, please
indicate your acceptance in the space provided for that purpose below. 
  

					
	Very truly yours,
	
	SQUARE 1 FINANCIAL, INC.
		
	By:	 	 /s/ Douglas H. Bowers

		 	Name:	 	Douglas Bowers
		 	Title:	 	President and Chief Executive Officer
		
	By:	 	 /s/ Robert I. Usdan

		 	Name:	 	Robert I. Usdan
		 	Title:	 	 Managing Member – W.R. Endicott III,

L.L.C. – General Partner of Endicott
 Opportunity Partners,
III, L.P.

 If the foregoing correctly sets forth the agreement between the Company and the Purchaser, please
indicate your acceptance in the space provided for that purpose below. 
  

					
	Very truly yours,
	
	SQUARE 1 FINANCIAL, INC.
		
	By:	 	 /s/ Douglas H. Bowers

		 	Name:	 	Douglas Bowers
		 	Title:	 	President and Chief Executive Officer
		
	By:	 	 /s/ James J. Lynch

		 	Name:	 	James J. Lynch
		 	Title:	 	Managing Partner
		
		 	 Patriot Financial Partners, L.P.

Patriot Financial Partners Parallel, L.P.

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