Document:

Exhibit 10.1

 Exhibit 10.1 
 Execution Copy 
 COMPANY SHAREHOLDER VOTING AGREEMENT 

This Company Shareholder Voting Agreement (this “Agreement”), dated as of December 18, 2012 is entered into by and
among Markel Corporation, a Virginia corporation (“Parent”), and each of the shareholders of Alterra Capital Holdings Limited, a Bermuda company (the “Company”), listed on Schedule A attached hereto (each, a
“Shareholder” and, collectively, the “Shareholders”). Capitalized terms used in this Agreement and not otherwise defined herein shall have the meanings assigned to them in the Agreement and Plan of Merger (as
defined below). 
 WHEREAS, concurrently with the execution and delivery of this Agreement, Parent, Merger Sub and the Company
have entered into an Agreement and Plan of Merger, dated as of the date hereof (the “Agreement and Plan of Merger”) (as the same may be amended or amended and restated from time to time in accordance with its terms); 

WHEREAS, each Shareholder is the beneficial owner (as defined in Rule 13d-3 of the Exchange Act, which meaning will apply for all
purposes of this Agreement whenever the term “beneficial” or “beneficially” is used) of (a) Company Common Shares (such shares, together with any other securities of the Company having voting rights acquired by such
Shareholder (including Company Common Shares acquired upon the exercise of any Company Stock Options or Company Warrants or upon the vesting of any Company Restricted Awards held by such Shareholder) after the Reference Date (as defined below)
through the Effective Time, being collectively referred to herein as the “Shares”), (b) Company Stock Options, (c) Company Restricted Awards and (d) Company Warrants, as of the date hereof (the “Reference
Date”) and as set forth opposite such Shareholder’s name on Schedule A attached hereto (“Schedule A”); 
 WHEREAS, obtaining the Company Merger Vote is a condition to the consummation of the Merger; and 
 WHEREAS, each Shareholder has agreed to enter into this Agreement in order to induce Parent to enter into the Agreement and Plan of Merger and to induce Parent to consummate, and to cause Merger Sub to
consummate, the transactions contemplated by the Agreement and Plan of Merger. 
 NOW, THEREFORE, in consideration of Parent and
the Merger Sub entering into the Agreement and Plan of Merger and of the mutual covenants and agreements contained herein and other good and valuable consideration, the adequacy of which is hereby acknowledged, and intending to be legally bound
hereby, the parties hereto agree as follows: 

 SECTION 1. Representations and Warranties of Each Shareholder. Each Shareholder
hereby represents and warrants to Parent as of the date of this Agreement as follows: 
 1.1 Title to the Shares. Such
Shareholder is the beneficial owner of the Company Common Shares, Company Stock Options, Company Restricted Shares and Company Warrants set forth opposite the name of such Shareholder on Schedule A, which, as of the Reference Date, constitute
all of the Company Common Shares and other securities convertible into or exercisable for any Company Common Shares, whether vested or unvested, owned of record or beneficially by such Shareholder. 

1.2 Voting Matters. Except to the extent (x) any such Shares are held by a trust and either Shareholder is not the trustee or
there are multiple trustees or (y) such Shareholder is deemed to be the beneficial owner of shares that are owned by another person, such Shareholder has the sole power to vote or cause to be voted the Shares set forth opposite the name of such
Shareholder on Schedule A on the matters specified in Section 4.1 hereof, free and clear of any and all claims, liens, encumbrances or restrictions on the right to vote such Shares, except (a) as may exist by reason of this
Agreement, (b) under applicable Law or (c) as referenced in Section 3.5 hereof. In furtherance (and not in limitation) of the foregoing, such Shareholder represents and warrants to Parent that all proxies heretofore given in respect
of any of its Shares, if any, are not irrevocable and that all such proxies have been properly revoked or are no longer in effect as of the date hereof. 
 1.3 Organization. To the extent such Shareholder is a corporation, partnership, limited liability company or other entity (“Entity”), such Shareholder is duly organized, validly
existing, and in good standing (or the equivalent concept to the extent applicable) under the laws of the jurisdiction of its incorporation, formation or organization. 
 1.4 Authority Relative to this Agreement. To the extent such Shareholder is an Entity, (a) such Shareholder has all requisite corporate, company, partnership or other power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to consummate the transactions contemplated hereby and (b) the execution and delivery of this Agreement by such Shareholder and the performance of its obligations
hereunder and the consummation of the transactions contemplated hereby have been duly and validly authorized by all necessary and appropriate corporate, partnership, company or other action on behalf of such Shareholder. To the extent that such
Shareholder is an individual, such Shareholder has the requisite legal capacity to execute and deliver this Agreement, to perform his or her obligations hereunder and to consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by such Shareholder and, assuming the due authorization, execution and delivery hereof by Parent, constitutes a valid and binding obligation of such Shareholder, enforceable against such Shareholder in

  
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accordance with its terms, except to the extent that enforcement is limited by bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar Laws of general applicability
relating to or affecting creditors’ rights or by general equitable principles (whether considered in a proceeding at law or in equity). 
 1.5 No Conflict. Except for any filings that may be required by applicable federal securities or antitrust laws, the execution and delivery of this Agreement by such Shareholder do not, and the
performance of its obligations hereunder and the consummation by such Shareholder of the transactions contemplated hereby will not, (a) require any consent or approval by, filing with, or notification to, any Governmental Entity or any other
Person by such Shareholder, (b) to the extent such Shareholder is an Entity, violate or conflict with or result in any breach of any provision of the organizational documents of such Shareholder, (c) violate or conflict with, or result in
any breach of or default (with or without notice or lapse of time or both) under, or give to any other Person (with or without notice or lapse of time or both) any right of termination, acceleration or cancellation of, or result in the creation of
any claims, liens, encumbrances or restrictions on the right to vote such Shares under, any provision of any agreement to which such Shareholder is a party or any instrument, permit, concession, franchise or license of such Shareholder or
(d) violate or conflict with any Law applicable to such Shareholder or to such Shareholder’s properties or assets, except in the case of the foregoing clauses (a), (c) and (d) only, for any of the foregoing as would not
reasonably be expected to materially impair or restrict such Shareholder’s ability to perform its obligations under this Agreement. 
 1.6 Reliance by Parent. Such Shareholder understands and acknowledges that Parent is entering into, and causing the Merger Sub to enter into, the Agreement and Plan of Merger in reliance upon such
Shareholder’s execution and delivery of this Agreement. 
 SECTION 2. Representations and Warranties of Parent.
Parent hereby represents and warrants to each Shareholder as of the date of this Agreement as follows: 
 2.1
Organization. Parent is a corporation duly incorporated, validly existing and in good standing under the laws of the state of Virginia. 
 2.2 Authority Relative to this Agreement. (a) Parent has all requisite corporate power and authority to execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby and (b) the execution and delivery of this Agreement by Parent and the performance of its obligations hereunder and the consummation of the transactions contemplated hereby have been duly and
validly authorized by all necessary and appropriate corporate action by the board of directors of Parent. This Agreement has been duly and validly executed and delivered by Parent and, assuming the due authorization, execution and delivery by each
of the Shareholders party hereto, constitutes a valid and binding obligation of 

  
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Parent, enforceable against Parent in accordance with its terms, except to the extent that enforcement is limited by bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and
similar Laws of general applicability relating to or affecting creditors’ rights or by general equitable principles (whether considered in a proceeding at law or in equity). 

2.3 No Conflict. Except for any filings that may be required by applicable federal securities or antitrust laws, the execution and
delivery of this Agreement by Parent do not, and the performance of its obligations hereunder and the consummation by Parent of the transactions contemplated hereby will not, (a) require any consent or approval by, filing with, or notification
to, any Governmental Entity or any other Person by Parent, (b) violate or conflict with or result in any breach of any provision of the articles of incorporation or by-laws of Parent, (c) violate or conflict with, or result in any breach
of or default (with or without notice or lapse of time or both) under, or give to any other Person (with or without notice or lapse of time or both) any right of termination, acceleration or cancellation of, any provision of any agreement to which
Parent is a party or any instrument, permit, concession, franchise or license of Parent, or (d) violate or conflict with any Law applicable to Parent or its properties or assets, except, in the case of the foregoing clauses (a), (c) and
(d) only for any of the foregoing as would not reasonably be expected to materially impair or restrict Parent’s ability to perform its obligations under this Agreement. 

SECTION 3. Additional Agreements. 
 3.1 Restriction on Transfer. Each Shareholder hereby covenants and agrees that, during the Voting Period, such Shareholder shall not sell, transfer, tender, assign, hypothecate or otherwise dispose
of (“Transfer”) any Shares or any interest therein or any other security convertible into or exercisable for any Company Common Shares, or create or permit to exist any additional security interest, lien, claim, pledge, option,
right of first refusal, limitation on voting rights, charge or other encumbrance of any nature (an “Encumbrance”) with respect to the Shares or any interest therein or any other security convertible into or exercisable for any
Company Common Shares; provided, that, any Shareholder may Transfer all or any portion of its Shares to (a) an Affiliate of such Shareholder, (b) such Shareholder’s spouse, immediate family members or lineal descendants or
(c) any trust or other entity, the beneficiaries or equity holders of which include only persons described in clause (b), in each case, if and only if the transferee of such Shares agrees in writing to be bound by the restrictions set forth in
this Agreement (each such transferee, a “Permitted Transferee”), or (d) to satisfy the payment of withholding income or other applicable taxes resulting from the vesting or exercising of any Company Stock Options or Company
Restricted Awards beneficially owned by such Shareholder. 

  
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 3.2 No Other Proxies. Each Shareholder hereby covenants and agrees, that during the
Voting Period, except as otherwise specifically contemplated or permitted by this Agreement (including Section 4.1), such Shareholder shall not, and shall not offer or agree to, grant any proxy or power of attorney with respect to, deposit into
a voting trust or enter into a voting arrangement, whether by proxy, voting agreement or otherwise, any Shares or any interest therein or any other securities convertible into or exercisable for any Company Common Shares; provided that nothing in
this Section 3.2 shall prevent such Shareholder from granting a proxy for Company’s 2013 Annual General Meeting of Shareholders with respect to matters not covered by Section 4.1. 

3.3 Additional Shares. In the event of a share dividend or distribution, or any change in the Company Common Shares by reason of
any share dividend or distribution, subdivision, recapitalization, reclassification, consolidation, conversion or the like, including the exchange of any securities convertible into or exercisable for any Company Common Shares, the term
“Shares” shall be deemed to refer to and include such shares as well as all such share dividends and distributions and any securities into which or for which any or all of the Shares may be changed or exchanged or which are received in
such transaction. For the avoidance of doubt, it is the intent of the parties that all Company Common Shares or other securities convertible into or exercisable for any Company Common Shares acquired by each Shareholder after the Reference Date
through the Voting Period be subject to the provisions of this Agreement. 
 3.4 Shareholder Capacity; Shareholder
Designees. All agreements and understandings made herein shall be made solely in a Shareholder’s capacity as a holder of the Shares. If a Shareholder is a director or officer of the Company, such agreements are not made in such
Shareholder’s capacity as a director or officer of the Company. For the avoidance of doubt, the parties acknowledge and agree that (a) each (i) Shareholder who is a director or (ii) other person who is a designee of a Shareholder
on the Company’s Board of Directors shall, in either case, be free to act in his or her capacity as a director of the Company in accordance with his or her duties to the Company, (b) nothing herein shall prohibit or restrict any person
described in clause (a) above from taking any action in facilitation of the exercise of his or her duties under the Agreement and Plan of Merger (including under Section 5.4 thereof) or otherwise, (c) nothing herein shall prohibit or
restrict any Shareholder who is an officer of the Company from taking any action, or failing to take any action, in his or her capacity as an officer of the Company and in facilitation of the exercise of his or her duties to the Company as such
Shareholder determines in good faith is required to comply with the direction of the Company’s Board of Directors and (d) no action taken by any person described in clauses (a) through (c) above acting in the capacities described
therein shall be deemed to be a breach or violation by a Shareholder of this Agreement. 
 3.5 Parent Acknowledgment.
Parent acknowledges and agrees that (a) the voting power otherwise conferred by the Shares under bye-law 51 of the Company’s bye-laws may be adjusted under bye-law 52 of the Company’s bye-laws (a “Limitation on Controlled
Shares”), (b) nothing in this Agreement shall prohibit, limit, 

  
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affect, modify, interpret or otherwise influence any determination made by the Company with respect to a Limitation on Controlled Shares and (c) if a Limitation on Controlled Shares is made
with respect to a Shareholder’s Shares, such Limitation on Controlled Shares shall not form the basis for any breach or violation by such Shareholder of this Agreement. Each Shareholder covenants and agrees that it shall promptly respond to any
request of the Company’s Board of Directors for information in the manner specified in bye-law 54 of the Company bye-laws. 

SECTION 4. Voting Agreement; Proxy. 
 4.1 Voting Agreement. Each Shareholder hereby agrees that, from the date of this Agreement until the earlier of (x) the Effective Time and (y) the termination of this Agreement (the
“Voting Period”), at any meeting of the shareholders of the Company or in any action by written consent of the shareholders of the Company, such Shareholder shall vote (or cause to be voted) all of its Shares: 

(a) in favor of approval and adoption of the Bye-Law Amendment, the Agreement and Plan of Merger, the Merger Agreement and
the Merger, and the other transactions contemplated thereby; 
 (b) in favor of adoption of any proposal in
respect of which the Company’s Board of Directors has (i) determined is designed to facilitate the consummation of the Merger, (ii) disclosed the determination described in clause (i) in the Joint Proxy Statement/Prospectus,
Other Company Filings or other written materials disseminated to all of the shareholders of the Company and (iii) recommended to be adopted by the shareholders of the Company; 

(c) against any action or agreement that has or would be reasonably likely to result in any conditions to the
Company’s obligations under Article VI of the Agreement and Plan of Merger not being fulfilled; 
 (d)
against any Takeover Proposal; and 
 (e) against any amendments to the memorandum of association or bye-laws of
the Company or other action, agreement, proposal or transaction involving the Company or any of its Subsidiaries that in any manner would reasonably be expected to materially impede, interfere with, delay, postpone or adversely affect the Merger or
the other transactions contemplated by the Agreement and Plan of Merger or change, in any manner, the voting rights of any class of shares of the Company; 

  
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 provided, that, if such Shareholder’s proxy has been granted to the Company under
Section 4.2 (and such proxy remains effective in accordance therewith), such Shareholder shall have no obligations under this Section 4.1 with respect to the meeting of the shareholders of the Company for which such proxy has been granted.

 4.2 Grant of Proxy. 
 (a) In furtherance of Section 4.1 of this Agreement, subject to Section 4.2(b) hereof and the proviso set forth below, each Shareholder hereby irrevocably grants to and appoints Parent and up to
two of Parent’s designated representatives (the “Authorized Parties”), and each of them individually, as such Shareholder’s proxy (with full power of substitution and resubstitution) for and in the name, place and stead of
such Shareholder, to attend all meetings of the shareholders of the Company and to vote the Shares at any meeting of the shareholders of the Company or in any action by written consent of the shareholders of the Company, during the Voting Period
solely on the matters and in the manner specified in Section 4.1 hereof, in each case subject to applicable Law (the “Proxy”); provided that in the case of any meeting of the shareholders of the Company during the Voting
Period at which a matter described in Section 4.1 is to be considered, such Shareholder’s grant of the Proxy contemplated by this Section 4.2(a) shall be effective if, and only if, such Shareholder has not delivered to the Secretary
of the Company at least three Business Days before such meeting a duly executed proxy card previously approved by Parent (such approval not to be unreasonably withheld or delayed) voting such Shareholder’s Shares in the manner specified in
Section 4.1. For the avoidance of doubt, the Proxy shall be effective for all actions by written consent of the shareholders of the Company during the Voting Period with respect to the matters set forth in Section 4.1. 

(b) It is hereby agreed that the Authorized Parties will use any Proxy granted by any Shareholder solely in accordance
with applicable Law and will only vote the Shares subject to such Proxy with respect to the matters and in the manner specified in Section 4.1 hereof. Subject to the foregoing sentence, following the grant of a Proxy under Section 4.2(a),
the vote of an Authorized Party shall control in any conflict between the vote by an Authorized Party of such Shares and any other vote by such Shareholder of its Shares during the Voting Period. 

(c) Each Shareholder hereby affirms that any Proxy granted under this Section 4.2 is given by such Shareholder in
connection with, and in consideration of, the execution of the Agreement and Plan of Merger by Parent, and that any such Proxy will be given to secure the performance of the duties of such Shareholder under this Agreement. 

  
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 (d) Any Proxy granted under this Section 4.2 by such Shareholder shall
be deemed to be coupled with an interest sufficient in law to support an irrevocable proxy and shall revoke any and all prior proxies granted by such Shareholder. Any Proxy granted hereunder shall terminate, and any underlying appointment shall
automatically be revoked and rescinded and of no force and effect, upon the termination of this Agreement. 
 (e)
Each Shareholder hereby acknowledges that the Company has agreed, under Section 5.1 of the Agreement and Plan of Merger, to recognize the Proxy at any meeting of the shareholders of the Company during the Voting Period. Each Shareholder hereby
further agrees that it will not intentionally take any action or fail to take any action with the primary purpose of causing the Company to fail to recognize such Proxy. 
 4.3 Other Voting. Each Shareholder shall vote on all issues other than those specified in Section 4.1 hereof that may come before a meeting of, or action by written consent by, the
shareholders of the Company in its sole discretion; provided that such vote or consent does not contravene the provisions of this Section 4. For the avoidance of doubt, Parent shall not have the right to be granted any proxy of a
Shareholder in connection with any such vote. 
 4.4 Lock-Up Agreement. Each Shareholder hereby covenants and agrees that
if the Closing occurs, it shall not, before the date that is three (3) months following the Closing Date (the “Lock-Up Period”), Transfer, or create or permit to exist any Encumbrance with respect to, any Parent Common Shares,
Company Converted Options, Company Converted Restricted Award or Company Converted Warrants beneficially owned by such Shareholder; provided, that, during the Lock-Up Period any Shareholder may Transfer all or any portion of such Parent
Common Shares (a) to a Permitted Transferee, (b) in any transaction required under applicable Law or approved by Parent or (c) to satisfy the payment of withholding income or other applicable taxes resulting from the vesting,
exercising, surrendering or rolling-over of any equity securities of Parent or the Company beneficially owned by such Shareholder. Notwithstanding anything to the contrary contained in this Agreement, if a Shareholder is an individual, the transfer
restrictions set forth in this Agreement shall not apply following such Shareholder’s death, termination of employment by Parent, the Company or any of their respective Subsidiaries without “Cause” or due to a “Change in
Control” or termination of employment by such Shareholder for “Good Reason” (in each case, as defined in the applicable agreements between the Company and such Shareholder). 

SECTION 5. Further Assurances. Each Shareholder shall, from time to time, perform such further acts and execute and deliver, or
cause to be executed and delivered, such additional or further consents, documents and other instruments as Parent may reasonably request in writing for the purpose of effectuating the matters covered by this Agreement or that are necessary to vest
in Parent the power to carry out and give effect to the provisions of this Agreement. 

  
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 SECTION 6. Termination. This Agreement and the obligations hereunder shall
automatically terminate on the first to occur of (a) the termination of the Agreement and Plan of Merger, (b) a written agreement between Parent and a Shareholder to terminate this Agreement (provided that in the case of this clause
(b) any such termination shall be effective only with respect to such Shareholder or Shareholders party to such agreement to terminate, and not any other shareholder of the Company party to this Agreement or a similar agreement with Parent;
provided further that any such termination that occurs after the Effective Time shall be deemed to be an amendment to Section 4.4 or any corresponding provision contained in such Shareholder’s voting agreement and shall be subject to
Section 7.7, below), (c) the conclusion of the Lock-Up Period and (d) the amendment of the Agreement and Plan of Merger to (i) reduce or change the form of the Consideration to be paid to such Shareholder in connection with the
Merger or (ii) provide for or otherwise result in disparate treatment of such Shareholder vis-a-vis the other shareholders of the Company with regard to the Consideration. The representations, warranties, obligations and agreements of the
parties contained in this Agreement shall not survive any termination of this Agreement; provided that if this Agreement is terminated under clause (a) of the preceding sentence, no party shall be relieved from its liability for any
willful and material breach of its obligations hereunder committed before such termination. For the avoidance of doubt: (A) the parties’ rights and obligations shall terminate with respect to Sections 4.1, 4.2 and 4.3 of this Agreement at
the Effective Time, and (B) the Voting Period will automatically end when this Agreement is terminated in accordance with this Section 6. 
 SECTION 7. Miscellaneous. 
 7.1 Appraisal Rights. Each Shareholder
hereby irrevocably and unconditionally waives, and agrees to prevent the exercise of, any rights to require appraisal of its Shares under Bermuda Law. 
 7.2 Publication. Each Shareholder hereby permits the Company and Parent to publish and disclose in any proxy statement or prospectus (including any document or schedule filed with the SEC) or any
other regulatory filings in connection with the Agreement and Plan of Merger such Shareholder’s identity and ownership of Company Common Shares, the other information set forth on Schedule A, and the nature of its commitments,
arrangements and understandings under this Agreement. 
 7.3 Expenses. All costs and expenses (including the fees and
expenses of investment bankers, accountants and counsel) incurred in connection with the transactions contemplated by this Agreement shall be paid by the party incurring such costs and expenses. 

7.4 Entire Agreement; No Third Party Beneficiaries. 

  
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 (a) This Agreement, including the Proxy and Schedule A, constitutes
the entire agreement and supersedes all prior agreements and understandings, both written and oral, among the parties with respect to the subject matter hereof; provided that if there is any conflict between this Agreement and the Agreement
and Plan of Merger, this Agreement shall control. This Agreement is intended to create a contractual relationship between each Shareholder, on the one hand, and Parent, on the other hand, and is not intended to create, and does not create, any
agency, partnership, joint venture or any like relationship among the parties hereto. Without limiting the generality of the foregoing, each Shareholder (i) is entering into this Agreement solely on its own behalf and, except as expressly set
forth in this Agreement, shall not have any obligation to perform on behalf of any other shareholder of the Company and (ii) by entering into this Agreement does not intend to form a “group” for purposes of Rule 13d-5(b)(1) of the
Exchange Act or any other similar provision of applicable Law with any other shareholder of the Company. Each Shareholder has acted independently regarding such Shareholder’s decision to enter into this Agreement. Parent acknowledges and agrees
that (A) absent an express statement in a representation, warranty, covenant or agreement to joint liability between or among a group of Shareholders specifically identified by name in such representation, warranty, covenant or agreement, all
representations, warranties, covenants and agreements of the Shareholders in this Agreement shall be made on a several, and not joint, basis and (B) in accordance with and subject to the foregoing, no Shareholder shall have any liability or
obligation for any breach or violation of, or failure to perform under, this Agreement by any other Shareholder. 

(b) This Agreement is not intended to, and shall not, confer upon any Person not a party hereto any rights or remedies
hereunder. 
 7.5 Assignment. A Shareholder may not assign any rights or delegate any obligations under this Agreement
without the prior written consent of Parent. Except as otherwise provided in Section 4.2 hereof, Parent may not assign any rights or delegate any obligations under this Agreement, in each case, with regard to a Shareholder without the prior
written consent of such Shareholder. Any such purported assignment or delegation made in violation of the foregoing shall be null and void. 
 7.6 Parties in Interest. This Agreement shall be binding upon, inure solely to the benefit of, and be enforceable by, the parties hereto and their successors and permitted assigns (including, for
the avoidance of doubt, a Shareholder’s heirs, legal representatives, successors and assigns). 

  
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 7.7 Amendment; No Waiver. This Agreement may not be amended except by an instrument
in writing between Parent and any Shareholder; provided, that, any amendment shall be effective only with respect to the Shareholder(s) executing such amendment; provided, further, that, in the event that Parent shall agree with
any other shareholder of the Company to amend this Agreement or a similar voting agreement, Parent shall offer all Shareholders the right to amend this Agreement on the same terms and conditions as those agreed upon between Parent and such other
shareholder. Neither the failure nor any delay by any party hereto in exercising any right, power or privilege under this Agreement will operate as a waiver of such right, power or privilege, and no single or partial exercise of any such right,
power or privilege will preclude any other or further exercise of such right, power or privilege or the exercise of any other right, power or privilege. In addition, (a) no claim or right arising out of this Agreement can be discharged by any
party, in whole or in part, by a waiver or renunciation of the claim or right unless in writing signed by such party, (b) no waiver that may be given by any party will be applicable except in the specific instance for which it is given and
(c) no notice to or demand on a party will be deemed to be a waiver of any obligation of such party and no notice from or demand by a party will be deemed to be a waiver of such party’s right to take further action without notice or demand
as provided in this Agreement. 
 7.8 Severability. If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of Law, or public policy, all other conditions and provisions of this Agreement shall nevertheless remain in full force and effect so long as the economic or legal substance of this Agreement is not
affected in any manner adverse to any party. Upon such determination that any term or other provision is invalid, illegal or incapable of being enforced, the parties hereto shall negotiate in good faith to modify this Agreement so as to effect the
original intent of the parties as closely as possible in a mutually acceptable manner in order that the terms of this Agreement remain as originally contemplated to the fullest extent possible. 

7.9 Notices. All notices and other communications hereunder shall be in writing and shall be deemed duly given (a) on the
date of delivery if delivered personally, (b) by facsimile upon confirmation of receipt or (c) on the second Business Day following the date of dispatch if delivered by a recognized express courier service. All notices hereunder shall be
delivered as set forth below or under such other instructions as may be designated in writing by the party to receive such notice. 
 if to Parent: 
 Markel Corporation 

4521 Highwoods Parkway 
 Glen Allen, Virginia 23060-6148 
 Attention: General Counsel 

  
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 with a copy (which shall not constitute notice) to: 

Debevoise & Plimpton LLP 
 919 Third Avenue 
 New York, NY 10022 

Attention: Nicholas Potter 
                  Gregory Gooding 
 if to a Shareholder, at its respective address set forth on Schedule A attached hereto. 
 7.10 Governing Law. This Agreement will be governed by, and construed in accordance with, the Laws of Bermuda, without regard to any principles of conflicts of law thereof that are not mandatorily
applicable by Law and would permit or require the application of the Laws of another jurisdiction. In furtherance of the foregoing, the parties hereby acknowledge and agree that it is their intent that the Chosen Courts (as defined below) not apply
the internal affairs doctrine for the purposes of any litigation, action, suit or other proceeding with respect to the subject matter hereof. 
 7.11 Specific Performance; Submission to Jurisdiction. The parties agree that money damages would be both incalculable and an insufficient remedy and that irreparable damage would occur if any of
the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached. It is accordingly agreed that, subject to the discretion of the Chosen Courts, the parties shall be entitled to an injunction or
other equitable relief to prevent breaches or violations of this Agreement and to enforce specifically the terms and provisions of this Agreement in any Chosen Court, this being in addition to any other remedy to which they are entitled at law or in
equity. Moreover, and in recognition of the foregoing, each of the parties hereby waives (a) any defense in any action for specific performance of this Agreement that a remedy at law would be adequate and (b) any requirement
under any law for any party to post security as a prerequisite to obtaining equitable relief. Each party irrevocably and unconditionally consents, agrees and submits to the jurisdiction of the Supreme Court of Bermuda (and appropriate appellate
courts therefrom) (the “Chosen Courts”), for the purposes of any litigation, action, suit or other proceeding with respect to the subject matter hereof. Each party agrees to commence any litigation, action, suit or proceeding
relating hereto only in the Supreme Court of Bermuda, or if such litigation, action, suit or other proceeding may not be brought in such court for reasons of subject matter jurisdiction, in the other appellate courts therefrom or other courts of
Bermuda. Each party irrevocably and unconditionally waives any objection to the laying of venue of any litigation, action, suit or proceeding with respect to the subject matter hereof in the Chosen Courts, and hereby further irrevocably and
unconditionally waives and agrees not to plead or claim in any such court that any such action, suit or proceeding brought in any such court has been brought in an inconvenient forum. Each party further irrevocably and unconditionally consents to
and grants any such court jurisdiction over the Person of 

  
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such parties and, to the extent legally effective, over the subject matter of any such dispute and agrees that mailing of process or other documents in connection with any such action or
proceeding in the manner provided in Section 7.9 hereof or in such other manner as may be permitted by applicable Law, shall be valid and sufficient service thereof. The parties agree that a final judgment in any such litigation, action, suit
or proceeding shall be conclusive and may be enforced in other jurisdictions by suit on the judgment or in any other manner provided by applicable Law. 
 7.12 Interpretation. The parties have participated jointly in negotiating and drafting this Agreement. If an ambiguity or a question of intent or interpretation arises, this Agreement shall be
construed as if drafted jointly by the parties, and no presumption or burden of proof shall arise favoring or disfavoring any party by virtue of the authorship of any provision of this Agreement. When a reference is made in this Agreement to
sections or subsections, such reference shall be to a section or subsection of this Agreement unless otherwise indicated. The phrases “the date of this Agreement”, “the date hereof” and terms of similar import, will be deemed to
refer to December 18, 2012. The headings contained in this Agreement are for reference purposes only and shall not affect in any way the meaning or interpretation of this Agreement. Whenever the words “include,” “includes” or
“including” are used in this Agreement, they shall be deemed to be followed by the words “without limitation.” The words “herein,” “hereof,” “hereunder” and words of similar import shall be deemed to
refer to this Agreement as a whole, including Schedule A hereto, and not to any particular provision of this Agreement. Any pronoun shall include the corresponding masculine, feminine and neuter forms. References to “party” or
“parties” in this Agreement mean Parent and each of the Shareholders, as the case may be. 
 7.13 Counterparts.
This Agreement may be executed in separate counterparts, each of which shall be considered one and the same agreement and shall become effective when each of the parties has delivered a signed counterpart to the other parties, it being understood
that all parties need not sign the same counterpart. Delivery of an executed signature page of this Agreement by facsimile transmission or electronic “.pdf” shall be effective as delivery of a manually executed counterpart hereof.

 [Rest of page intentionally left blank] 

  
 13 

 IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement to be executed as
of the date first above written. 
  

			
	MARKEL CORPORATION
		
	By:	 	 
	Name:	 	
	Title:	 	

  
 14 

 
			
	
	[SHAREHOLDER]
	
	 

  
 15 

 Schedule A 

 

									
	 Name and Address
	  	Number of
Company Common
Shares Owned as of
[•]	  	Number of
Company Stock
Options Owned as
of [•]	  	Number of
Company Restricted
Shares Owned as of
[•]	  	Number of Company
Warrants Owned as of [•]Exhibit 10.2

 Exhibit 10.2 
 Execution Copy 
 PARENT SHAREHOLDER VOTING AGREEMENT 

This Parent Shareholder Voting Agreement (this “Agreement”), dated as of December 18, 2012 is entered into by and
among Alterra Capital Holdings Limited, a Bermuda company (the “Company”), and each of the shareholders of Markel Corporation, a Virginia corporation (“Parent”), listed on Schedule A attached hereto (each, a
“Shareholder” and, collectively, the “Shareholders”). Capitalized terms used in this Agreement and not otherwise defined herein shall have the meanings assigned to them in the Agreement and Plan of Merger (as
defined below). 
 WHEREAS, concurrently with the execution and delivery of this Agreement, Parent, Merger Sub and the Company
have entered into an Agreement and Plan of Merger, dated as of the date hereof (the “Agreement and Plan of Merger”) (as the same may be amended or amended and restated from time to time in accordance with its terms); 

WHEREAS, each Shareholder is the beneficial owner (as defined in Rule 13d-3 of the Exchange Act, which meaning will apply for all
purposes of this Agreement whenever the term “beneficial” or “beneficially” is used) of (a) Parent Common Shares (such shares, together with any other securities of the Parent having voting rights acquired by such
Shareholder (including Parent Common Shares acquired upon the vesting of any Parent Restricted Awards (as defined below) held by such Shareholder) after the Reference Date (as defined below) through the Effective Time, being collectively referred to
herein as the “Shares”), (b) restricted Parent Common Shares, and (c) restricted stock units payable in Parent Common Shares (“Parent Restricted Awards”), as of the date hereof (the “Reference
Date”) and as set forth opposite such Shareholder’s name on Schedule A attached hereto (“Schedule A”); 
 WHEREAS, obtaining the Parent Merger Vote is a condition to the consummation of the Merger; and 
 WHEREAS, each Shareholder has agreed to enter into this Agreement in order to induce the Company to enter into the Agreement and Plan of Merger and to induce the Company to consummate, and to cause Merger
Sub to consummate, the transactions contemplated by the Agreement and Plan of Merger. 
 NOW, THEREFORE, in consideration of
Parent and the Merger Sub entering into the Agreement and Plan of Merger and of the mutual covenants and agreements contained herein and other good and valuable consideration, the adequacy of which is hereby acknowledged, and intending to be legally
bound hereby, the parties hereto agree as follows: 

 SECTION 1. Representations and Warranties of Each Shareholder. Each Shareholder
hereby represents and warrants to the Company as of the date of this Agreement as follows: 
 1.1 Title to the Shares.
Such Shareholder is the beneficial owner of the Parent Common Shares, Parent Restricted Shares and Parent Restricted Awards set forth opposite the name of such Shareholder on Schedule A, which, as of the Reference Date, constitute all of the
Parent Common Shares and other securities convertible into or exercisable for any Parent Common Shares, whether vested or unvested, owned of record or beneficially by such Shareholder. 

1.2 Voting Matters. Except to the extent (x) any such Shares are held by a trust and either Shareholder is not the trustee
or there are multiple trustees or (y) such Shareholder is deemed to be the beneficial owner of shares that are owned by another person, such Shareholder has the sole power to vote or cause to be voted the Shares set forth opposite the name of
such Shareholder on Schedule A on the matters specified in Section 4.1 hereof, free and clear of any and all claims, liens, encumbrances or restrictions on the right to vote such Shares, except (a) as may exist by reason of this
Agreement or (b) under applicable Law. In furtherance (and not in limitation) of the foregoing, such Shareholder represents and warrants to the Company that all proxies heretofore given in respect of any of its Shares, if any, are not
irrevocable and that all such proxies have been properly revoked or are no longer in effect as of the date hereof. 
 1.3
Authority Relative to this Agreement. Such Shareholder has the requisite legal capacity to execute and deliver this Agreement, to perform his or her obligations hereunder and to consummate the transactions contemplated hereby. This Agreement
has been duly and validly executed and delivered by such Shareholder and, assuming the due authorization, execution and delivery hereof by the Company, constitutes a valid and binding obligation of such Shareholder, enforceable against such
Shareholder in accordance with its terms, except to the extent that enforcement is limited by bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar Laws of general applicability relating to or affecting creditors’
rights or by general equitable principles (whether considered in a proceeding at law or in equity). 
 1.4 No Conflict.
Except for any filings that may be required by applicable federal securities or antitrust laws, the execution and delivery of this Agreement by such Shareholder do not, and the performance of its obligations hereunder and the consummation by such
Shareholder of the transactions contemplated hereby will not, (a) require any consent or approval by, filing with, or notification to, any Governmental Entity or any other Person by such Shareholder, (b) to the extent such Shareholder is
an Entity, violate or conflict with or result in any breach of any provision of the organizational documents of such Shareholder, (c) violate or conflict with, or result in any breach of or default (with or without notice or lapse of time or
both) under, or give to any other Person (with or without notice or lapse of time or both) any right of 

  
 2 

 
termination, acceleration or cancellation of, or result in the creation of any claims, liens, encumbrances or restrictions on the right to vote such Shares under, any provision of any agreement
to which such Shareholder is a party or any instrument, permit, concession, franchise or license of such Shareholder or (d) violate or conflict with any Law applicable to such Shareholder or to such Shareholder’s properties or assets,
except in the case of the foregoing clauses (a), (c) and (d) only, for any of the foregoing as would not reasonably be expected to materially impair or restrict such Shareholder’s ability to perform its obligations under this
Agreement. 
 1.5 Reliance by the Company. Such Shareholder understands and acknowledges that the Company is entering
into the Agreement and Plan of Merger in reliance upon such Shareholder’s execution and delivery of this Agreement. 

SECTION 2. Representations and Warranties of the Company. The Company hereby represents and warrants to each Shareholder as of the
date of this Agreement as follows: 
 2.1 Organization. The Company is an exempted company duly organized, validly
existing and in good standing under the laws of Bermuda. 
 2.2 Authority Relative to this Agreement. (a) The
Company has all requisite corporate power and authority to execute and deliver this Agreement, to perform its obligations hereunder and to consummate the transactions contemplated hereby and (b) the execution and delivery of this Agreement by
the Company and the performance of its obligations hereunder and the consummation of the transactions contemplated hereby have been duly and validly authorized by all necessary and appropriate corporate action by the board of directors of the
Company. This Agreement has been duly and validly executed and delivered by the Company and, assuming the due authorization, execution and delivery by each of the Shareholders party hereto, constitutes a valid and binding obligation of the Company,
enforceable against the Company in accordance with its terms, except to the extent that enforcement is limited by bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar Laws of general applicability relating to or
affecting creditors’ rights or by general equitable principles (whether considered in a proceeding at law or in equity). 

2.3 No Conflict. Except for any filings that may be required by applicable federal securities or antitrust laws, the execution
and delivery of this Agreement by the Company do not, and the performance of its obligations hereunder and the consummation by the Company of the transactions contemplated hereby will not, (a) require any consent or approval by, filing with, or
notification to, any Governmental Entity or any other Person by the Company, (b) violate or conflict with or result in any breach of any provision of the articles of incorporation or by-laws of the Company, (c) violate or conflict with, or
result in any breach of or default (with or without notice or lapse of time or both) under, or give to any other Person (with or without notice or lapse 

  
 3 

 
of time or both) any right of termination, acceleration or cancellation of, any provision of any agreement to which the Company is a party or any instrument, permit, concession, franchise or
license of the Company, or (d) violate or conflict with any Law applicable to the Company or its properties or assets, except, in the case of the foregoing clauses (a), (c) and (d) only for any of the foregoing as would not reasonably
be expected to materially impair or restrict the Company’s ability to perform its obligations under this Agreement. 

SECTION 3. Additional Agreements. 
 3.1 Restriction on Transfer. Each Shareholder hereby covenants and agrees that, during the Voting Period, such Shareholder shall not sell, transfer, tender, assign, hypothecate or otherwise dispose
of (“Transfer”) any Shares or any interest therein or any other security convertible into or exercisable for any Parent Common Shares, or create or permit to exist any additional security interest, lien, claim, pledge, option, right
of first refusal, limitation on voting rights, charge or other encumbrance of any nature (an “Encumbrance”) with respect to the Shares or any interest therein or any other security convertible into or exercisable for any Parent
Common Shares; provided, that, any Shareholder may Transfer all or any portion of its Shares to (a) an Affiliate of such Shareholder, (b) such Shareholder’s spouse, immediate family members or lineal descendants, (c) any
trust or other entity, the beneficiaries or equity holders of which include only persons described in clause (b), in each case, if and only if the transferee of such Shares agrees in writing to be bound by the restrictions set forth in this
Agreement (each such transferee, a “Permitted Transferee”), or (d) to satisfy the payment of withholding income or other applicable taxes resulting from the vesting or exercising of any Parent Restricted Awards beneficially
owned by such Shareholder. Notwithstanding the foregoing, any Shares held by a trust as of the date hereof may be distributed to the beneficiaries thereof or otherwise Transferred (x) to the extent required by the terms of the applicable trust
agreement or (y) in order to make distributions from the trust consistent with past practice; provided that, the total number of Shares that may be Transferred by all Shareholders pursuant to this sentence, together with the corresponding
sentence included in Section 4.4, shall not exceed 50,000 Shares in the aggregate. 
 3.2 No Other Proxies. Each
Shareholder hereby covenants and agrees, that during the Voting Period, except as otherwise specifically contemplated or permitted by this Agreement (including Section 4.1), such Shareholder shall not, and shall not offer or agree to, grant any
proxy or power of attorney with respect to, deposit into a voting trust or enter into a voting arrangement, whether by proxy, voting agreement or otherwise, any Shares or any interest therein or any other securities convertible into or exercisable
for any Parent Common Shares; provided that nothing in this Section 3.2 shall prevent such Shareholder from granting a proxy for Parent’s 2013 Annual Meeting of Shareholders with respect to matters not covered by Section 4.1.

  
 4 

 3.3 Additional Shares. In the event of a share dividend or distribution, or any
change in the Parent Common Shares by reason of any share dividend or distribution, subdivision, recapitalization, reclassification, consolidation, conversion or the like, including the exchange of any securities convertible into or exercisable for
any Parent Common Shares, the term “Shares” shall be deemed to refer to and include such shares as well as all such share dividends and distributions and any securities into which or for which any or all of the Shares may be changed or
exchanged or which are received in such transaction. For the avoidance of doubt, it is the intent of the parties that all Parent Common Shares or other securities convertible into or exercisable for any Parent Common Shares acquired by each
Shareholder after the Reference Date through the Voting Period be subject to the provisions of this Agreement. 
 3.4
Shareholder Capacity; Shareholder Designees. All agreements and understandings made herein shall be made solely in a Shareholder’s capacity as a holder of the Shares. If a Shareholder is a director or officer of Parent, such agreements
are not made in such Shareholder’s capacity as a director or officer of Parent. For the avoidance of doubt, the parties acknowledge and agree that (a) each (i) Shareholder who is a director shall be free to act in his or her capacity
as a director of Parent in accordance with his or her duties to Parent, (b) nothing herein shall prohibit or restrict any person described in clause (a) above from taking any action in facilitation of the exercise of his or her duties
under the Agreement and Plan of Merger (including under Section 5.4 thereof) or otherwise, (c) nothing herein shall prohibit or restrict any Shareholder who is an officer of Parent from taking any action, or failing to take any action, in
his or her capacity as an officer of Parent and in facilitation of the exercise of his or her duties to Parent as such Shareholder determines in good faith is required to comply with the direction of Parent’s Board of Directors and (d) no
action taken by any person described in clauses (a) through (c) above acting in the capacities described therein shall be deemed to be a breach or violation by a Shareholder of this Agreement. 

SECTION 4. Voting Agreement; Proxy. 
 4.1 Voting Agreement. Each Shareholder hereby agrees that, from the date of this Agreement until the earlier of (x) the Effective Time and (y) the termination of this Agreement (the
“Voting Period”), at any meeting of the shareholders of Parent or in any action by written consent of the shareholders of Parent, such Shareholder shall vote (or cause to be voted) all of its Shares: 

(a) in favor of the Parent Share Issuance; 

(b) in favor of adoption of any proposal in respect of which the Parent’s Board of Directors has (i) determined
is designed to facilitate the consummation of the Parent Share Issuance, (ii) disclosed the determination described in clause (i) in the Joint Proxy Statement/Prospectus, Other Parent Filings or other written materials disseminated to all
of the shareholders of Parent and (iii) recommended to be adopted by the shareholders of Parent; 

  
 5 

 (c) against any action or agreement that has or would be reasonably likely
to result in any conditions to Parent’s obligations under Article VI of the Agreement and Plan of Merger not being fulfilled; 
 (d) against any Takeover Proposal; and 
 (e) against any
amendments to the articles of incorporation or by-laws of Parent or other action, agreement, proposal or transaction involving Parent or any of its Subsidiaries that in any manner would reasonably be expected to materially impede, interfere with,
delay, postpone or adversely affect the Parent Share Issuance or the other transactions contemplated by the Agreement and Plan of Merger or change, in any manner, the voting rights of any class of shares of Parent; 

provided, that, if such Shareholder’s proxy has been granted to the Company under Section 4.2 (and such proxy remains effective in
accordance therewith), such Shareholder shall have no obligations under this Section 4.1 with respect to the meeting of the shareholders of Parent for which such proxy has been granted. 

4.2 Grant of Proxy. 
 (a) In furtherance of Section 4.1 of this Agreement, subject to Section 4.2(b) hereof and the proviso set forth below, each Shareholder hereby irrevocably grants to and appoints the Company and
up to two of the Company’s designated representatives (the “Authorized Parties”), and each of them individually, as such Shareholder’s proxy (with full power of substitution and resubstitution) for and in the name, place
and stead of such Shareholder, to attend all meetings of the shareholders of Parent and to vote the Shares at any meeting of the shareholders of Parent or in any action by written consent of the shareholders of Parent, during the Voting Period
solely on the matters and in the manner specified in Section 4.1 hereof, in each case subject to applicable Law (the “Proxy”); provided that in the case of any meeting of the shareholders of Parent during the Voting
Period at which a matter described in Section 4.1 is to be considered, such Shareholder’s grant of the Proxy contemplated by this Section 4.2(a) shall be effective if, and only if, such Shareholder has not delivered to the Secretary
of Parent at least three Business Days before such meeting a duly executed proxy card previously approved by the Company (such approval not to be unreasonably withheld or delayed) voting such Shareholder’s Shares in the manner specified in
Section 4.1. For the avoidance of doubt, the Proxy shall be effective for all actions by written consent of the shareholders of Parent during the Voting Period with respect to the matters set forth in Section 4.1. 

  
 6 

 (b) It is hereby agreed that the Authorized Parties will use any Proxy
granted by any Shareholder solely in accordance with applicable Law and will only vote the Shares subject to such Proxy with respect to the matters and in the manner specified in Section 4.1 hereof. Subject to the foregoing sentence, following
the grant of a Proxy under Section 4.2(a), the vote of an Authorized Party shall control in any conflict between the vote by an Authorized Party of such Shares and any other vote by such Shareholder of its Shares during the Voting Period.

 (c) Each Shareholder hereby affirms that any Proxy granted under this Section 4.2 is given by such
Shareholder in connection with, and in consideration of, the execution of the Agreement and Plan of Merger by the Company, and that any such Proxy will be given to secure the performance of the duties of such Shareholder under this Agreement.

 (d) Any Proxy granted under this Section 4.2 by such Shareholder shall be deemed to be coupled with an
interest sufficient in law to support an irrevocable proxy and shall revoke any and all prior proxies granted by such Shareholder. Any Proxy granted hereunder shall terminate, and any underlying appointment shall automatically be revoked and
rescinded and of no force and effect, upon the termination of this Agreement. 
 (e) Each Shareholder hereby
acknowledges that Parent has agreed, under Section 5.1 of the Agreement and Plan of Merger, to recognize the Proxy at any meeting of the shareholders of Parent during the Voting Period. Each Shareholder hereby further agrees that it will not
intentionally take any action or fail to take any action with the primary purpose of causing Parent to fail to recognize such Proxy. 
 4.3 Other Voting. Each Shareholder shall vote on all issues other than those specified in Section 4.1 hereof that may come before a meeting of, or action by written consent by, the
shareholders of Parent in its sole discretion; provided that such vote or consent does not contravene the provisions of this Section 4. For the avoidance of doubt, the Company shall not have the right to be granted any proxy of a
Shareholder in connection with any such vote. 
 4.4 Lock-Up Agreement. Each Shareholder hereby covenants and agrees
that if the Closing occurs, it shall not, before the date that is three (3) months following the Closing Date (the “Lock-Up Period”), Transfer, or create or permit to exist any Encumbrance with respect to, any Parent Common
Shares, Parent Restricted Shares or Parent Restricted Award beneficially owned by such Shareholder; provided, that, during the Lock-Up Period any Shareholder may Transfer all or any portion of such Parent Common Shares (a) to a Permitted
Transferee, (b) in any transaction required under applicable Law or approved by Parent or (c) to satisfy the payment of withholding 

  
 7 

 
income or other applicable taxes resulting from the vesting or exercising of any Parent Restricted Awards beneficially owned by such Shareholder. Notwithstanding anything to the contrary
contained in this Agreement, the transfer restrictions set forth in this Agreement shall not apply following a Shareholder’s death, termination of employment by Parent, the Company or any of their respective Subsidiaries without
“Cause” or due to a “Change in Control” or termination of employment by such Shareholder for “Good Reason” (in each case, as defined in the applicable agreements between the Company and such Shareholder).
Notwithstanding the foregoing, any Shares held by a trust as of the date hereof may be distributed to the beneficiaries thereof or otherwise Transferred (x) to the extent required by the terms of the applicable trust agreement or (y) in
order to make distributions from the trust consistent with past practice; provided that, the total number of Shares that may be Transferred by all Shareholders pursuant to this sentence, together with the corresponding sentence included in
Section 3.1, shall not exceed 50,000 Shares in the aggregate. 
 SECTION 5. Further Assurances. Each Shareholder
shall, from time to time, perform such further acts and execute and deliver, or cause to be executed and delivered, such additional or further consents, documents and other instruments as the Company may reasonably request in writing for the purpose
of effectuating the matters covered by this Agreement or that are necessary to vest in the Company the power to carry out and give effect to the provisions of this Agreement. 
 SECTION 6. Termination. This Agreement and the obligations hereunder shall automatically terminate on the first to occur of (a) the termination of the Agreement and Plan of Merger, (b) a
written agreement between the Company and a Shareholder to terminate this Agreement (provided that in the case of this clause (b) any such termination shall be effective only with respect to such Shareholder or Shareholders party to such
agreement to terminate, and not any other shareholder of Parent party to this Agreement or a similar agreement with the Company; provided further that any such termination that occurs after the Effective Time shall be deemed to be an amendment to
Section 4.4 or any corresponding provision contained in such Shareholder’s voting agreement and shall be subject to Section 7.7, below), (c) the conclusion of the Lock-Up Period and (d) the amendment of the Agreement and
Plan of Merger to increase or change the form of the Consideration to be paid to shareholders of the Company in connection with the Merger. The representations, warranties, obligations and agreements of the parties contained in this Agreement shall
not survive any termination of this Agreement; provided that if this Agreement is terminated under clause (a) of the preceding sentence, no party shall be relieved from its liability for any willful and material breach of its obligations
hereunder committed before such termination. For the avoidance of doubt: (A) the parties’ rights and obligations shall terminate with respect to Sections 4.1, 4.2 and 4.3 of this Agreement at the Effective Time, and (B) the Voting
Period will automatically end when this Agreement is terminated in accordance with this Section 6. 

  
 8 

 SECTION 7. Miscellaneous. 

7.1 Publication. Each Shareholder hereby permits the Company and Parent to publish and disclose in any proxy statement or
prospectus (including any document or schedule filed with the SEC) or any other regulatory filings in connection with the Agreement and Plan of Merger such Shareholder’s identity and ownership of Parent Common Shares, the other information set
forth on Schedule A, and the nature of its commitments, arrangements and understandings under this Agreement. 
 7.2
Expenses. All costs and expenses (including the fees and expenses of investment bankers, accountants and counsel) incurred in connection with the transactions contemplated by this Agreement shall be paid by the party incurring such costs and
expenses. 
 7.3 Entire Agreement; No Third Party Beneficiaries. 

(a) This Agreement, including the Proxy and Schedule A, constitutes the entire agreement and supersedes all prior
agreements and understandings, both written and oral, among the parties with respect to the subject matter hereof; provided that if there is any conflict between this Agreement and the Agreement and Plan of Merger, this Agreement shall
control. This Agreement is intended to create a contractual relationship between each Shareholder, on the one hand, and the Company, on the other hand, and is not intended to create, and does not create, any agency, partnership, joint venture or any
like relationship among the parties hereto. Without limiting the generality of the foregoing, each Shareholder (i) is entering into this Agreement solely on its own behalf and, except as expressly set forth in this Agreement, shall not have any
obligation to perform on behalf of any other shareholder of Parent and (ii) by entering into this Agreement does not intend to form a “group” for purposes of Rule 13d-5(b)(1) of the Exchange Act or any other similar provision of
applicable Law with any other shareholder of Parent. Each Shareholder has acted independently regarding such Shareholder’s decision to enter into this Agreement. The Company acknowledges and agrees that (A) absent an express statement in a
representation, warranty, covenant or agreement to joint liability between or among a group of Shareholders specifically identified by name in such representation, warranty, covenant or agreement, all representations, warranties, covenants and
agreements of the Shareholders in this Agreement shall be made on a several, and not joint, basis and (B) in accordance with and subject to the foregoing, no Shareholder shall have any liability or obligation for any breach or violation of, or
failure to perform under, this Agreement by any other Shareholder. 
 (b) This Agreement is not intended to, and
shall not, confer upon any Person not a party hereto any rights or remedies hereunder. 

  
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 7.4 Assignment. A Shareholder may not assign any rights or delegate any obligations
under this Agreement without the prior written consent of the Company. Except as otherwise provided in Section 4.2 hereof, the Company may not assign any rights or delegate any obligations under this Agreement, in each case, with regard to a
Shareholder without the prior written consent of such Shareholder. Any such purported assignment or delegation made in violation of the foregoing shall be null and void. 
 7.5 Parties in Interest. This Agreement shall be binding upon, inure solely to the benefit of, and be enforceable by, the parties hereto and their successors and permitted assigns (including, for
the avoidance of doubt, a Shareholder’s heirs, legal representatives, successors and assigns). 
 7.6 Amendment; No
Waiver. This Agreement may not be amended except by an instrument in writing between the Company and any Shareholder; provided, that, any amendment shall be effective only with respect to the Shareholder(s) executing such amendment;
provided, further, that, in the event that the Company shall agree with any other shareholder of Parent to amend this Agreement or a similar voting agreement, the Company shall offer all Shareholders the right to amend this Agreement
on the same terms and conditions as those agreed upon between the Company and such other shareholder. Neither the failure nor any delay by any party hereto in exercising any right, power or privilege under this Agreement will operate as a waiver of
such right, power or privilege, and no single or partial exercise of any such right, power or privilege will preclude any other or further exercise of such right, power or privilege or the exercise of any other right, power or privilege. In
addition, (a) no claim or right arising out of this Agreement can be discharged by any party, in whole or in part, by a waiver or renunciation of the claim or right unless in writing signed by such party, (b) no waiver that may be given by
any party will be applicable except in the specific instance for which it is given and (c) no notice to or demand on a party will be deemed to be a waiver of any obligation of such party and no notice from or demand by a party will be deemed to
be a waiver of such party’s right to take further action without notice or demand as provided in this Agreement. 
 7.7
Severability. If any term or other provision of this Agreement is invalid, illegal or incapable of being enforced by any rule of Law, or public policy, all other conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is not affected in any manner adverse to any party. Upon such determination that any term or other provision is invalid, illegal or incapable of being enforced, the
parties hereto shall negotiate in good faith to modify this Agreement so as to effect the original intent of the parties as closely as possible in a mutually acceptable manner in order that the terms of this Agreement remain as originally
contemplated to the fullest extent possible. 

  
 10 

 7.8 Notices. All notices and other communications hereunder shall be in writing and
shall be deemed duly given (a) on the date of delivery if delivered personally, (b) by facsimile upon confirmation of receipt or (c) on the second Business Day following the date of dispatch if delivered by a recognized express
courier service. All notices hereunder shall be delivered as set forth below or under such other instructions as may be designated in writing by the party to receive such notice. 

if to the Company: 
 Alterra Capital Holdings Limited 
 2 Front Street 

Hamilton HM 11 Bermuda 
 Attention: Chief Financial Officer 
 with a copy (which shall not constitute
notice) to: 
 Akin Gump Strauss Hauer & Feld LLP 

One Bryant Park 

New York, New York 10036 
 Attention: Kerry E. Berchem, Esq. 

                 Jeffrey L. Kochian, Esq. 

if to a Shareholder, at its respective address set forth on Schedule A attached hereto. 

7.9 Governing Law. This Agreement will be governed by, and construed in accordance with, the Laws of the State of Virginia,
without regard to any principles of conflicts of law thereof that are not mandatorily applicable by Law and would permit or require the application of the Laws of another jurisdiction. In furtherance of the foregoing, the parties hereby acknowledge
and agree that it is their intent that the Chosen Courts (as defined below) not apply the internal affairs doctrine for the purposes of any litigation, action, suit or other proceeding with respect to the subject matter hereof. 

7.10 Specific Performance; Submission to Jurisdiction. The parties agree that money damages would be both incalculable and an
insufficient remedy and that irreparable damage would occur if any of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached. It is accordingly agreed that, subject to the discretion of
the Chosen Courts, the parties shall be entitled to an injunction or other equitable relief to prevent breaches or violations of this Agreement and to enforce specifically the terms and provisions of this Agreement in any Chosen Court, this being in
addition to any other remedy to which they are entitled at law or in equity. Moreover, and in recognition of the foregoing, each of the parties hereby waives (a) any defense in any action for specific performance of this Agreement

  
 11 

 
that a remedy at law would be adequate and (b) any requirement under any law for any party to post security as a prerequisite to obtaining equitable relief. Each party irrevocably and
unconditionally consents, agrees and submits to the jurisdiction of the state or federal courts in the City of Richmond or the County of Henrico, Virginia (the “Chosen Courts”), for the purposes of any litigation, action, suit or
other proceeding with respect to the subject matter hereof. Each party agrees to commence any litigation, action, suit or proceeding relating hereto only in the Chosen Courts. Each party irrevocably and unconditionally waives any objection to the
laying of venue of any litigation, action, suit or proceeding with respect to the subject matter hereof in the Chosen Courts, and hereby further irrevocably and unconditionally waives and agrees not to plead or claim in any such court that any such
action, suit or proceeding brought in any such court has been brought in an inconvenient forum. Each party further irrevocably and unconditionally consents to and grants any such court jurisdiction over the Person of such parties and, to the extent
legally effective, over the subject matter of any such dispute and agrees that mailing of process or other documents in connection with any such action or proceeding in the manner provided in Section 7.9 hereof or in such other manner as may be
permitted by applicable Law, shall be valid and sufficient service thereof. The parties agree that a final judgment in any such litigation, action, suit or proceeding shall be conclusive and may be enforced in other jurisdictions by suit on the
judgment or in any other manner provided by applicable Law. 
 7.11 Interpretation. The parties have participated
jointly in negotiating and drafting this Agreement. If an ambiguity or a question of intent or interpretation arises, this Agreement shall be construed as if drafted jointly by the parties, and no presumption or burden of proof shall arise favoring
or disfavoring any party by virtue of the authorship of any provision of this Agreement. When a reference is made in this Agreement to sections or subsections, such reference shall be to a section or subsection of this Agreement unless otherwise
indicated. The phrases “the date of this Agreement”, “the date hereof” and terms of similar import, will be deemed to refer to December 18, 2012. The headings contained in this Agreement are for reference purposes only and
shall not affect in any way the meaning or interpretation of this Agreement. Whenever the words “include,” “includes” or “including” are used in this Agreement, they shall be deemed to be followed by the words
“without limitation.” The words “herein,” “hereof,” “hereunder” and words of similar import shall be deemed to refer to this Agreement as a whole, including Schedule A hereto, and not to any particular
provision of this Agreement. Any pronoun shall include the corresponding masculine, feminine and neuter forms. References to “party” or “parties” in this Agreement mean the Company and each of the Shareholders, as the case may
be. 

  
 12 

 7.12 Counterparts. This Agreement may be executed in separate counterparts, each of
which shall be considered one and the same agreement and shall become effective when each of the parties has delivered a signed counterpart to the other parties, it being understood that all parties need not sign the same counterpart. Delivery of an
executed signature page of this Agreement by facsimile transmission or electronic “.pdf” shall be effective as delivery of a manually executed counterpart hereof. 
 [Rest of page intentionally left blank] 

  
 13 

 IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement to be executed as
of the date first above written. 
  

			
	ALTERRA CAPITAL HOLDINGS LIMITED
		
	By:	 	 
	Name:	 	
	Title:	 	

  
 14 

 
	
	[SHAREHOLDER]
	
	  

  
 15 

 Schedule A 

 

							
	 Name and Address
	  	Number of Parent Common
Shares Owned as of
December 18, 2012*	  	Number of Parent
Restricted Awards Owned as of
December 18, 
2012	  	Number of Parent
Restricted Shares Owned as of
December 18, 
2012
	 Alan I. Kirshner

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	25,558	  	0	  	0
				
	 J. Alfred Broaddus, Jr.

4114 Hanover Avenue

Richmond, VA 23221
	  	1,361	  	0	  	181
				
	 Douglas C. Eby

1530 33rd Street, NW

Washington, DC 20007
	  	224	  	0	  	181
				
	 Stewart M. Kasen

7101 Dubonnet Drive

Boca Raton, FL 33433
	  	6,148	  	0	  	181
				
	 Lemuel E. Lewis

9111 River Crescent

Suffolk, VA 23433
	  	2,918	  	0	  	181
				
	 Anthony F. Markel

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	117,565	  	0	  	0
				
	 Steven A. Markel

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	312,595	  	0	  	0
				
	 Darrell D. Martin

161 West Square Place

Richmond, VA 23238
	  	23,337	  	0	  	181
				
	 Jay M. Weinberg

20320 Fairway Oaks Dr.,

Apt. 333

Boca Raton, FL 33434
	  	3,664	  	0	  	181
				
	 Debora J. Wilson

4770 E. Conway Dr., NW

Atlanta, GA 30327
	  	1,160	  	0	  	181
				
	 F. Michael Crowley

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	2,473	  	5,581	  	0
				
	 Thomas S. Gayner

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	26,738	  	9,655	  	0
				
	 Richard R. Whitt, III

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	6,680	  	3,295	  	0
				
	 Gerard Albanese

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	6,826	  	3,290	  	0

							
	 Name and Address
	  	Number of Parent Common
Shares Owned as of
December 18, 2012*	  	Number of Parent
Restricted Awards Owned as of
December 18, 
2012	  	Number of Parent
Restricted Shares Owned as of
December 18, 
2012
				
	 Bradley J. Kiscaden

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	3,395	  	2,078	  	0
				
	 Anne G. Waleski

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	2,151	  	1,532	  	0
				
	 Britton L. Glisson

4521 Highwoods Pkwy

Glen Allen, VA 23060
	  	10,650	  	2,628	  	0

 * Includes shares held in trusts, if applicable, where individual is a trustee, beneficiary or partial beneficiary, even
if shares can be beneficially disclaimed. Includes shares held by spouses, if applicable, even can be beneficially disclaimed. Includes shares held in 401(k)s, if applicable, as of September 30, 2012.

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