<PAGE>
                                                                    Exhibit 10.9

October 16, 2006

Joseph S. Tibbetts, Jr.
116 Farm Street
Dover, MA 02030

Dear Joe,

This letter confirms our offer of employment to you as Senior Vice President and
Chief Financial Officer with Sapient Corporation ("Sapient" or the "Company") in
our offices located in Cambridge, Massachusetts. Your anticipated start date is
October 30, 2006. If you accept the offer of employment, your base compensation
will consist of an annualized base salary of $350,000 ($29,166 per month), paid
in accordance with Sapient's regular payroll practices. This offer is contingent
upon satisfactory results of a background check, which will include (but not
necessarily be limited to) a check on your educational and criminal history, as
well as your execution of the Sapient Confidentiality Agreement and the Sapient
Fair Competition Agreement, as described below.

In addition to your base salary, you will be granted 400,000 restricted stock
units (the "Performance RSUs") of Sapient Corporation common stock. The grant
date will be the first NASDAQ trading day in the month immediately following
your start date. Your Performance RSUs will vest in the following amounts if and
when the average 30-day closing price of the Company common stock on the Nasdaq
Stock Market (or principal market upon which the common stock trades) equals or
exceeds the following per share prices, provided you are still employed by the
Company on each such vesting date:

<TABLE>
<CAPTION>
PERFORMANCE RSUS VESTED                    SHARE PRICE
-----------------------                    -----------
<S>                                        <C>
        100,000                               $5.00
        100,000                               10.00
        100,000                               15.00
        100,000                               20.00
</TABLE>

Any Performance RSUs that have not vested on the fourth anniversary of the date
of grant shall be forfeited.

In addition to the Performance RSUs, you will be granted 75,000 restricted stock
units (the "Time-Based RSUs") of common stock (the "Initial Grant"). The grant
date for the Initial Grant will be the first NASDAQ trading day in the month
immediately following your start date. Your Initial Grant of Time-Based RSUs
will vest in two tranches: 25,000 shares will vest on the last day of the 18th
month following the grant date and 50,000 shares will vest on the day before the
3d anniversary of the grant date, provided you are still employed by the Company
on each such vesting date. You will receive an additional RSU Award of 75,000
Time-Based RSUs on each of the first and second anniversaries of the grant date
of the Initial Grant, on terms identical to those of the Initial Grant. You must
sign the Sapient standard form of RSU agreement in order for all grants of
Performance RSUs and Time-Based RSUs to become effective. This standard form
will be sent electronically by Sapient's 3rd party

<PAGE>

equity administrator within sixty days of the Grant Date. The RSUs are subject
to the terms and conditions in such RSU agreement and any other restrictions or
limitations generally applicable to equity held by Company executives or
otherwise required by law.

You will also be eligible to earn up to four weeks paid vacation per calendar
year on a pro rata basis, in accordance with Sapient's current vacation policy.

You will be eligible to participate in Sapient's medical, dental, disability and
life insurance plans during your employment, subject to the terms of the
applicable plan documents and generally applicable Company policies. The
effective date of your participation in Sapient's medical, dental, disability
and life insurance plans will be the first day of the month following your start
date. The eligibility requirements and terms and conditions of the medical,
dental, disability and life insurance plans are set forth in their respective
summary plan descriptions, which are available from the Benefits Team.

In addition to your base compensation, you will be eligible to begin
participation in Sapient's 2006 bonus program. Specifically, you will be
eligible to participate in the 2006 Performance Bonus Plan (the "Bonus Plan"),
subject to the specific terms of the Bonus Plan, as well as in any future
incentive programs that may be made available to you in the Company's discretion
and for which you are eligible. You will be on the Director/VP Track, as
described in the Bonus Plan. As a participant on the Director/VP Track under the
current Bonus Plan, you will have a target bonus opportunity for 2006 of
$175,000 (guaranteed pro rated for the partial year of service), subject to the
specific terms and conditions of the Bonus Plan. Your target bonus for 2007 will
be no less than $175,000. Any amounts payable under the Bonus Plan shall be
payable not later than two and one-half months following the end of the fiscal
year for which the bonus was earned.

During your employment, you will also be eligible to participate in Sapient's
Employee Stock Purchase Plan ("ESPP") and 401(k) Savings Plan pursuant to the
terms of those plans. At this time, the ESPP permits a qualified participant to
purchase Sapient stock from the company at a 15% discount through payroll
deductions of up to 10% of a participant's cash compensation. At this time,
under the 401(k) Plan, Sapient may contribute $0.25 for every $1.00 you
contribute to your Sapient 401(k) account, up to a maximum Sapient contribution
of $1,250 per year. You will receive more detailed information about these and
other Sapient benefit programs at the beginning of your employment. Any
additional questions about our benefits can be directed to the Benefits Team.

Should a Change in Control, as defined below, occur and/or your employment with
Sapient end for one of the reasons specified below, Sapient agrees to provide
you with severance/Change in Control payments and benefits as detailed below;
provided, however, that any obligation of the Company to provide you with any
such pay and benefits is expressly conditioned upon your signing and returning
to the Company a timely and effective release of claims in the form provided by
the Company, and upon your continued compliance with your obligations to the
Company, including but not limited to your obligations pursuant

                                       2
<PAGE>

to the Sapient Confidentiality Agreement and the Sapient Fair Competition
Agreement. For purposes of this letter, the general terms of such payments and
benefits are set forth below, although it is contemplated that these terms will
be memorialized in a separate agreement to be signed as soon as practicable
after you commence employment. The triggers for your entitlement to Change in
Control and post-termination payments and benefits are as follows. It is
understood and agreed that if your employment terminates for any reason other
than those set forth specifically below, you will not be eligible for any
severance or Change in Control payments or benefits, and your participation in
all of the Company's benefit plans shall terminate pursuant to the terms of the
applicable plans, except for any right you may have to continue medical or
dental plan participation pursuant to applicable law:

TERMINATION BY THE COMPANY FOR CAUSE OR BY YOU FOR GOOD REASON OTHER THAN UPON A
CHANGE IN CONTROL

      -     Termination by the Company other than for "Cause," where "Cause" is
            defined as:

            (a)   Your malfeasance or negligence in the performance of your
                  duties;

            (b)   Fraud or dishonesty by you with respect to the Company;

            (c)   Your conviction of or plea of nolo contendre to any felony or
                  other crime involving moral turpitude;

            (d)   Your material breach of any provision of this Agreement, the
                  Sapient Confidentiality Agreement or the Sapient Fair
                  Competition Agreement.

      -     Termination by you for "Good Reason," where "Good Reason" is defined
            as any of the following, without your consent:

            (a)   Material diminution in the nature or scope of your
                  responsibilities, a change in your title or reporting
                  requirements from those in effect on your start date
                  (excluding an isolated, insubstantial and inadvertent action
                  not taken in bad faith and which is remedied by the Company
                  promptly after receipt of notice by you thereof);

            (b)   Reducing your base salary;

            (c)   Failing to maintain your participation in the Company's
                  long-term incentive plan, as amended from time to time in the
                  Company's sole discretion, in a manner that is consistent with
                  the participation of other senior executives at the Company;

            (d)   Failing to maintain the aggregate amount of your benefits
                  under or relative level of participation in the Company's
                  employee benefit or retirement plans, policies, practices, or
                  arrangements in which you participate as of your start date;

                                       3
<PAGE>

            (e)   Relocation of your principal place of business to a distance
                  greater than 50 miles from the location in effect on your
                  start date.

Within fifteen (15) days after one of the termination events above, provided no
benefits are payable to you under a separate severance plan or agreement as a
result of such termination:

      (1) you will be entitled to receive a lump-sum payment in cash equal to
150% of your then current base salary and target bonus, subject to applicable
withholding and other customary deductions;

      (2) you will receive a lump-sum payment equivalent to the pro-rata portion
of your target bonus for the year in which termination occurs, subject to
applicable withholding and other customary deductions;

      (3) if there are any Time-Based RSUs outstanding on the date of
termination, vesting will accelerate such that the next vesting date will be
deemed to have occurred on the date of termination, and any Time-Based RSUs that
do not vest on such date will be forfeited (e.g., if termination occurs within
the first 18 months following the grant date, 25,000 shares will vest and 50,000
will be forfeited; if after the first 18 months but before the third anniversary
of the grant date, the next 50,000 will vest);

      (4) if, during the 90 trading days following your termination by the
Company without Cause or by you for Good Reason, the 30-day average closing
price of the common stock reaches a threshold that had not been reached upon the
termination date, 100,000 shares (or the applicable multiple of 100,000 shares,
depending on the threshold that is achieved) of Performance RSUs will vest and
be payable to you. All other Performance RSUs will be forfeited;

      (5) for a period of eighteen months following the date of termination, you
will be entitled to participate in Sapient's medical, dental, disability and
life insurance plans, subject to any employee contribution applicable to you on
the date of termination; and your 401(k) plan will continue to vest, provided
you are eligible to continue such participation and vesting under applicable law
and plan terms.

DEFINITION OF "CHANGE IN CONTROL"

A "Change in Control" shall be deemed to have occurred if any two or more of the
following events occur:

      -     Acquisition by a person or group (other than the two current largest
            stockholders and their affiliates) of more than 50% of the
            outstanding shares of common stock,

      -     A change in a majority of the non-employee directors over a one-year
            period (other than by reason of election or nomination by directors
            constituting a majority of the directors on your start date or
            directors who were chosen by those directors),

                                       4
<PAGE>

      -     A merger, consolidation or other corporate transaction that results
            in shareholders before the transaction constituting less than 65% of
            the shareholders following the transaction,

      -     A liquidation or a sale of all or substantially all of Sapient's
            assets, or

      -     A determination by the Board of Directors that a change in control
            has occurred.

In the event of a Change in Control while you are employed hereunder, all of
your outstanding Performance RSUs and Time-Based RSUs shall become vested
effective as of the date of such Change in Control, provided, however, that no
benefits are payable to you under a separate plan or agreement as a result of
such Change in Control.

In addition, if a Change in Control occurs during your employment hereunder and
within two (2) years following such Change in Control your employment is
terminated by the Company without Cause (as defined above) or by you for Good
Reason (as defined below), then in lieu of any other severance payments or
benefits, pursuant to this agreement or otherwise, the Company will pay you a
lump-sum payment in cash equal to two hundred percent (200%) of your
then-current base salary and target bonus, subject to applicable withholding and
other customary deductions, within fifteen (15) days after such termination.

For purposes of termination by you for Good Reason following a Change in
Control, Good Reason is defined as any of the following, without your consent:

      (a)   Material diminution in the nature or scope of your responsibilities,
            duties or authority from those in effect on your start date,
            excluding an isolated, insubstantial and inadvertent action not
            taken in bad faith and which is remedied by the Company promptly
            after receipt of notice by yout thereof;

      (b)   Reducing your base salary;

      (c)   Reducing your targeted annual bonus opportunity;

      (d)   Failing to maintain your participation in the Company's long-term
            incentive plan, as amended from time to time in the Company's sole
            discretion, in a manner that is consistent with the participation of
            other senior executives at the Company;

      (e)   Failing to maintain the aggregate amount of your benefits under or
            relative level of participation in the Company's employee benefit or
            retirement plans, policies, practices, or arrangements in which you
            participate as of your start date;

      (f)   Relocation of the your principal place of business to a distance
            greater than 50 miles from the location in effect on your start
            date.

                                       5
<PAGE>

The severance and Change in Control payments and benefits described above are
intended to be exempt from Section 409A of the Internal Revenue Code of 1986, as
amended ("Section 409A"), pursuant to the short-term deferral provisions
thereof, and shall be construed accordingly. In the event that the Company
reasonably determines that such payments are subject to Section 409A, any and
all such amounts that constitute deferred compensation subject to Section 409A
and that would (but for this sentence) be payable within six months following
separation from service (as defined in Section 409A), shall instead be paid on
the date that follows the date of such separation from service by six (6)
months.

During your hiring process, we may disclose to you certain of our trade secrets
or confidential or proprietary information. In order to assure the
confidentiality of such trade secrets and confidential or proprietary
information, you agree that you will hold in confidence, and not disclose to
anyone outside of Sapient, any of our trade secrets, confidential or proprietary
information, or similar information that you may receive from us with respect to
Sapient or any of our clients or prospective clients.

Please note that the conditions of this offer letter are specific to you and,
therefore, Sapient requests that the terms be held in confidence.

On or before your first day of work, we will expect you to sign the enclosed
standard agreements: the Sapient Confidentiality Agreement and the Sapient Fair
Competition Agreement. Your offer of employment with Sapient is contingent upon
your signing and returning these two agreements to us before your first day of
work.

Please note that all references in this letter agreement to Sapient's option
plans, vacation policy, other policies and procedures, medical, dental,
disability and life insurance plans, bonus plans, commission plans, compensation
plans, ESPP, 401(k) plan and other benefit programs are to those plans,
policies, procedures and programs as they are currently in effect and/or as any
of them may be modified at any time in Sapient's sole discretion. Sapient may
alter, add to, modify or delete any of these plans, policies or programs at any
time as it, in its sole judgment, determines to be appropriate, without resourse
by you. In the event of any conflict between information contained in this
letter and in any of the plan, policy or program documents, the plan, policy or
program documents will control.

This letter and your response are not meant to constitute a contract of
employment for a specific term. If you accept Sapient's offer of employment, you
will be employed on an "at-will" basis. That means you are free, at any time,
for any reason, to end your employment with Sapient and that Sapient may do the
same.

This offer constitutes the entire agreement between you and the Company and
supersedes all prior understandings, negotiations and agreements, whether
written or oral, between you and Sapient as to the subject matter covered by
this offer letter, excluding only the Sapient

                                       6
<PAGE>

Confidentiality Agreement and the Sapient Fair Competition Agreement. It may be
amended or modified only by a writing signed by you and an expressly authorized
representative of the Company.

On your first day of employment or shortly after your first week, you will need
to attend SapientStart training for people new to Sapient. One of our
SapientStart associates will contact you at least 2 weeks prior to your start
date to get you prepared for your SapientStart training logistics, travel,
accommodations etc.

We look forward to welcoming you and having you as a member of the Sapient team.
If you agree with these terms, please sign below and return a signed copy of
this letter to ____________________ by ______.

Congratulations and welcome aboard!

Best regards,

/s/ Michael White
-----------------
    Hiring

Accepted:

/s/ Joseph S. Tibbetts, Jr.
---------------------------
Signature

Print Name: Joseph S. Tibbetts, Jr.
Date: 10/16/06

                                       7