<PAGE>

                                                                   EXHIBIT 10.19

October 1, 1999

Mr. John Stopper
346 Dan's Highway
New Canaan, CT 06840

Dear John:

We are delighted to make the conditional offer to you to become an employee of
Greenwich Technology Partners, Inc. (the "Company") as a Vice President - New
Markets, contained in our offering letter to you dated this date. Your start
date is August 3, 1999 and your office location will be 43 Gatehouse Rd.,
Stamford, CT 06902. This offer is valid for 15 business days from the above date
and is contingent upon successful completion of our background checks.

We are very proud of our corporate culture. We believe that open communication
between the Company and its employees and treating each other fairly and with
respect are critical to our success and to creating an environment in which we
are able to enjoy our work. Consequently, we want your assurance that should
there ever come a time during your employment with the Company that you are
dissatisfied with any aspect of your employment, you will communicate such
dissatisfaction to the person to whom you directly report, or, if that is not
comfortable for you, to any other manager of the Company, including the Chief
Executive Officer.

1.  Major Terms
    -----------

    A.  Services
        --------

        While you are employed by the Company, you, will devote your entire and
        exclusive business and professional time, attention, energy, loyalty and
        skill to the business of the Company. In addition, you will use your
        reasonable efforts to preserve for the Company the goodwill of customers
        and others with whom the Company establishes business relationships
        during your employment and to advance the reputation of the Company. You
        shall comply with and perform such directions and duties in relation to
        the business and affairs of the Company requested of you by the Company.

    B.  Compensation
        ------------

        In consideration of all of the services to be rendered by you to the
        Company, while you are employed by the Company, the Company will pay to
        you a salary of $150,000 per annum. Such salary shall be payable on the
        15th and 30th day of each month in arrears, pro rated for the initial
        period worked. The Company shall have the right to deduct from your
        compensation all taxes and other legally required payroll deductions and
        withholdings. Your salary structure and promotions shall be reviewed
        annually by a member of senior management.
<PAGE>

                                      -2-

        Pursuant to Connecticut Wage laws, you are an exempt employee and
        therefore not eligible under State requirements to receive overtime pay.

        Variable Compensation: While you are employed by the Company, variable
        compensation for each of the first three (3) months will be $12,500 of
        monthly nonrecoverable draw, and during months four (4) through six (6)
        will be $12,500 of monthly recoverable draw, based on a target variable
        compensation of $150,000 per annum.

    C.  Options
        -------

        You will be granted an option to purchase up to 168,600 shares of the
        Company's common stock, upon approval of the Company's Board of
        Directors. The option will be issued pursuant to the terms of the
        Company's 1997 Stock Plan and a stock option agreement to be entered
        into between the Company and you. In addition, you will be eligible to
        receive an additional 112,400 shares of the Company's common stock, in
        accordance with the Company's standard stock option grant policy. This
        Section 1.C. is for informational purposes only.

    D.  Employment At Will
        ------------------

        You will be an employee-at-will; your employment may be terminated by
        you or the Company at any time, with or without cause. Neither this
        letter agreement, any employee handbook, or any other document of the
        Company gives you any contractual right, either express or implied, to
        remain in the employ of the Company.

    E.  Use of Company Property
        -----------------------

        You will not use the Company's premises, facilities, or equipment for
        personal purposes.

    F.  Moonlighting and Competitive Activity
        -------------------------------------

        You covenant and agree that, during non-business hours, you shall not
        engage in any activity related to, competitive with, or in the business
        of, the Company, without the prior written consent of the Company. Such
        activities shall include, but not be limited to designing intranet or
        internet networks, network consulting, maintenance, repair,
        troubleshooting or systems design and/or installation (a "Competitive
        Activity"). If you are unsure whether a particular activity would
        violate the aforesaid covenant, you shall seek the advice of a senior
        officer of the Company. You hereby accept said employment and agree
        faithfully to perform said duties and render said services for the term
        of your employment.

2.  Right to Change Pay Practices, Policies, Procedures and Benefits. The
    ----------------------------------------------------------------
    Company shall have the right, at any time without prior notice, to change,
    modify, amend, or terminate
<PAGE>

                                      -3-

    any pay practice, employment policy or procedure, or employment benefit plan
    or program in effect upon the commencement of your employment or adopted
    subsequently. You will be entitled to participate on the same basis with all
    other employees in similar positions of the Company in the Company's
    standard benefits package generally available to other employees in similar
    positions of the Company, including medical and dental coverage, a 401K
    plan, short term and long term disability, and life insurance.

3.  Representations and Warranties. You represent and warrant that: you are not
    ------------------------------
    under any obligation to any third party which could interfere with your
    performance under this letter agreement; and your performance of your
    obligations to the Company during your employment with the Company will not
    breach any agreement by which you are bound not to disclose any proprietary
    information.

4.  Inventions.
    ----------

    i.   You will as soon as practicable disclose to the Company all Inventions
         (as herein defined). "Inventions" shall mean all ideas, potential
         marketing and sales relationships, inventions, research, plans for
         products and services, marketing plans, software (including, without
         limitation, source code), know-how, trade secrets, information, data,
         developments, discoveries, improvements, modifications, technology, and
         designs, whether or not subject to patent or copyright protection,
         made, conceived, expressed, developed, or actually or constructively
         reduced to practice by you solely or jointly with others during your
         employment with the Company, which refer to, are suggested by, or
         result from any work which you may do during your employment, or from
         any information obtained from the Company.

    ii.  The Inventions shall be the exclusive property of the Company, and are
         hereby assigned by you to the Company; the Company shall have the
         exclusive right to use the Inventions for all purposes without
         additional compensation to you. At the Company's expense, you will
         assist the Company in every proper way to protect the Inventions
         throughout the world, including, without limitation, executing in favor
         of the Company patent, copyright, and other applications and
         assignments relating to the Inventions.

5.  Confidential Information.
    -------------------------

    i.   You will not disclose, give, sell, publish or otherwise use, either
         during your employment by the Company or after the termination of your
         employment, except in the performance of your duties for the benefit of
         the Company, any Confidential Information (as herein defined).
         "Confidential Information" shall mean, but not be limited to, all of
         the Company's proprietary information, technical data, technology,
         process, trade secrets, and know-how, other intellectual property
         rights, strategies, financial statements or other financial
         information, forecasts, operations, business plans, prices, discounts,
         products, product specifications, designs, plans data, ideas or
         information contained in the
<PAGE>

                                      -4-

         Company's Business Strategy Overview and Career Advancement Manual
         which is disclosed to you, which you may acquire or develop, or which
         you may observe in the course of your employment by the Company and
         which at the time of disclosure is not previously known by you and not
         known or used by others in the trade generally, does not become
         generally available to the trade through no fault of yours, and does
         not become rightfully available to you on a non-confidential basis from
         a source other than the Company, including, without limitation,
         research, product plans, customer lists, markets, software,
         developments, inventions, processes, formulas, technology, designs,
         drawings, marketing and other plans, and financial data and
         information. "Confidential Information" shall also mean information
         received by the Company from customers of the Company or other third
         parties subject to a duty to keep confidential and financial, pricing,
         and credit information regarding customers, clients, or vendors of the
         Company. Upon termination of your employment, you shall promptly
         deliver to the Company, in whatever form or medium, all files,
         drawings, blueprints, specifications, reports, notebooks, and other
         materials containing any Confidential Information which are in your
         possession or control.

    ii.  shall not discuss with, or disclose to, other employees of the Company,
         the terms of your Offer Package, including, but not limited to,
         compensation, grant of options or other special arrangements. Such
         information shall be considered Confidential Information, and
         disclosure of such Confidential Information shall be grounds for your
         dismissal from the Company.

6.  Restrictive Covenants.
    ---------------------

    A.  Covenants Against Competition and Solicitation.
        ----------------------------------------------

        From the date hereof until one year following the date of termination
        (for any reason) of your (the "Term of Commitment") employment with the
        Company (or any of its affiliates) (the "Termination Date"), without the
        prior written consent of the Company, you will not, directly or
        indirectly:

             i.   persuade or attempt to persuade any customer, client, supplier
                  or distributor of the Company to cease doing business with the
                  Company, or to reduce the amount of business it does with the
                  Company;

             ii.  persuade or attempt to persuade any potential customer,
                  client, supplier or distributor to which the Company has made
                  a presentation, or with which the Company had been having
                  discussions, not to do business with the Company, or to
                  undertake with any other person, individual, corporation,
                  partnership, trust, joint venture, business or unincorporated
                  organization (a "Person") a Competitive Activity;
<PAGE>

                                      -5-

             iii. solicit for itself or any Person other than the Company the
                  business of any Person which is a customer, client, supplier
                  or distributor of the Company, or was a customer, client,
                  supplier or distributor of the Company or become retained or
                  employed by, as a consultant, employee or otherwise, of any of
                  the foregoing, except as permitted herein;

             iv.  persuade or attempt to persuade any employee of the Company,
                  or any individual who was an employee of the Company during
                  the two years prior to the Termination Date, to leave the
                  employ of the Company, or to become employed by, as a
                  consultant, employee or otherwise, of any Person engaged in a
                  Competitive Activity.

     B. Geographic Scope.
        -----------------

     For purposes of paragraph 6A, the geographic scope of the restrictive
     covenants contained therein, shall be 150 miles from any Company branch
     office or the Company's headquarters.

7.  Injunctive Relief and Severability.
    -----------------------------------

    i.   You agree that the remedy at law for any breach of the provisions of
         this letter agreement shall be inadequate and the Company shall be
         entitled to injunctive or other equitable relief in addition to any
         other remedy it might have.

    ii.  The Company and you agree and acknowledge that the covenant not to
         compete and the right of first refusal described are made in
         consideration of substantial compensation payable under this letter
         agreement. In consequence of this the Company and you agree and
         acknowledge that the duration, scope, and geographic area included in
         such covenant not to compete are fair, reasonable, necessary, and
         appropriate, and will not prevent you from engaging in profitable
         business activities or employment. Nevertheless, should a court
         determine that such duration, scope, or geographic areas are not
         reasonable, such restrictions shall be interpreted, modified, or
         rewritten to include as much of such duration, scope, or geographic
         areas as will render such restrictions valid and enforceable.

    iii. The Company and you intend to and do hereby confer jurisdiction to
         enforce this letter agreement upon the courts of any jurisdiction
         within the geographical scope of the agreements contained herein. In
         the event that the courts of any one or more of such jurisdictions
         shall hold such agreements wholly or partly unenforceable by reason of
         the breadth of such scope or otherwise, it is the intention of the
         Company and you that such determination shall not bar or in any way
         affect the Company's right to relief hereunder in the courts of any
         other jurisdiction within the geographical scope of any such agreement,
         as to breaches of such agreements in such other respective
         jurisdictions, the above agreements as they relate to each jurisdiction
         being, for this purpose, severable into independent agreements.
<PAGE>

                                      -6-

8.  Severability.
    ------------

    In the event any of the provisions of this letter agreement shall be held by
    a court or other tribunal of competent jurisdiction to be unenforceable, the
    other provisions of this letter agreement shall remain in full force and
    effect.

9.  Survival.
    --------

    All terms and conditions of this letter agreement which should by their
    nature survive the termination of your employment with the Company shall so
    survive.

10. Governing Law.
    -------------

    This letter shall be governed by, construed and enforced in accordance with
    the internal laws of the State of Connecticut governing agreements made and
    to be fully performed therein, without giving effect to conflict of law
    principles.

11. Notices.
    -------

    All notices, requests, consents and other communications required or
    permitted hereunder shall be in writing and shall be hand delivered or
    mailed by certified or registered mail, return receipt requested, addressed
    as follows:

    i.    if to the Company, at Greenwich Technology Partners, Inc., 43
          Gatehouse Road, Stamford, CT 06902, Attention: Director of Legal
          Affairs.

    ii.   if to you, at the address set forth above or in any such case, at such
          other addresses as may have been furnished to any party by the other
          party in writing in the manner herein provided. Any notice or other
          communication so addressed and so mailed shall be seemed to have been
          given when mailed, and if hand delivered shall be deemed to have been
          given when delivered.

12. Waivers and Modifications.
    -------------------------

    This letter agreement may be modified, and the rights and remedies of any
    provision hereof may be waived, only in writing, signed by each of the
    Company, and you. No waiver by either party of any breach by the other of
    any provision hereof shall be deemed to be a waiver of any later or other
    breach thereof or as a waiver of any such or other provision of this letter
    agreement. This agreement sets forth all of the terms of the understandings
    between the parties with reference to the subject matter set forth herein
    may not be waived, changed, discharged or terminated orally or by any course
    of dealing between the parties, but only by an instrument in writing signed
    by the party against whom any waiver, change, discharge or termination is
    sought. Each of the Company and you hereby acknowledges and agrees that any
    prior arrangements, agreements or
<PAGE>

                                      -7-

    understandings relating to your employment with the Company and/or any of
    its affiliates is hereby terminated and extinguished in its entirety.

13. Assignment.
    ----------

    This Agreement shall be binding upon and inure to the benefit of the Company
    and its successors and assigns. This Agreement is not assignable by you and
    your right to receive payment for your services is hereby expressly agreed
    to be non-assignable and nontransferable, except as otherwise specifically
    provided herein.

14. Change in Control.
    -----------------

    In the event that following a Change in Control (defined below) your
    employment with the Company is terminated by you for Good Reason (defined
    below) or by the Company, other than for Good Cause (defined below), (each a
    "Termination Event"), you will be provided with Severance Pay (defined
    below) and there will be an automatic acceleration of the vesting of 25% of
    the options granted to you, on the terms and conditions set forth herein. If
    following a Change in Control a Termination Event occurs in the first twelve
    (12) months of your employment, 70,250 of the options granted to you shall
    automatically become exercisable. This Section is for informational purposes
    and is pursuant to the terms of the Stock Option Agreement.

    If following a Change in Control there is a Termination Event which occurs
    after the date of your employment but prior to six months of said date, the
    Company will provide six months' Severance Pay. If following a Change in
    Control there is a Termination Event which occurs after the sixth month
    anniversary date of your employment date but prior to one year anniversary
    of your employment date, the Company will provide nine months' Severance
    Pay. If following a Change in Control there is a Termination Event which
    occurs after the twelfth month anniversary date of your employment date of
    the Change in Control, the Company will provide twelve (12) months'
    Severance Pay. The Severance Pay will be paid no later than thirty (30) days
    after termination and paid in one lump sum unless a schedule of payments is
    agreed to by you.

    Definitions. The following definitions are applicable only to the extent the
    -----------
    above Change in Control occurs. In no instance shall these definitions apply
    outside of a Change in Control with the Company.

    a.  Severance Pay: an amount equal to the monthly average sum of (i) your
        -------------
    monthly base salary plus (ii) your monthly incentive or variable
    compensation amount being paid to you in the previous quarter prior to any
    Termination Event.

    b.  Change in Control; the first to occur of the following:
        -----------------

        (i)   the Company is merged, consolidated or reorganized into or with
              another corporation or other legal person, and as a result of such
              merger, consolidation or reorganization less than a majority of
              the combined
<PAGE>

                                      -8-

              voting power of the then-outstanding securities of
              the combined corporation or person immediately after such
              transaction are held in the aggregate by the holders of the
              combined voting power of the then-outstanding securities entitled
              to vote generally in the election of directors of the Company
              ("Voting Stock") immediately prior to such transaction;

        (ii)  the Company sells or otherwise transfers all or substantially all
              of its assets to any other corporation or other legal person, and
              less than a majority of the combined voting power of the then-
              outstanding securities of such corporation or person immediately
              after such sale or transfer is held in the aggregate by the
              holders of the Voting Stock of the Company immediately prior to
              such sale or transfer;

        (iii) any person (as the term "person" is used in Section 13(d)(3) or
              Section 14(d)(2) of the Securities Exchange Act of 1934) has
              become the beneficial owner (as the term "beneficial owner" is
              defined under Rule 13d-3 or any successor rule or regulation
              promulgated under the Securities Exchange Act of 1934 Act) of
              securities representing 50% or more of the Voting Stock.

     c.   Good Cause: any of
          ----------

          (i)   Your willful and substantial misconduct with respect to the
                business and affairs of the Company;

          (ii)  Your gross neglect of duties, dishonesty, deliberate disregard
                of any material rule or policy of the Company or the commission
                by you of any other action with the intent to injury the
                Company; or

          (iii) Your commission of an act involving embezzlement or fraud or
                commission of a felony.

     d.   Good Reason: the occurrence of any of the following: (i) the
          -----------
          assignment to you of duties materially inconsistent with the status of
          your position with the Company or the material diminution in the
          nature or status of your duties and powers and your responsibilities
          in connection with such duties and powers, (ii) a requirement by the
          Company that you relocate your primary residence outside of the area
          comprising a 50 mile radius around the then current location of such
          residence (the "Area"), (iii) the reduction of your base salary; or
          (iv) a change in the composition of the plan pursuant to which you are
          eligible for incentive or variable compensation such that your ability
          to earn such incentive compensation is significantly diminished.

If the Company proposes to engage in any transaction which is intended to be
accounted for as a pooling-of-interests, and in the event that the provisions of
this Agreement, or any actions of the
<PAGE>

                                      -9-

Board of Directors of the Company taken in connection with such transaction, are
determined by the Company's or the acquiring company's independent public
accounts to cause such transaction to fail to be accounted for as a pooling-of-
interests, then such provisions or actions shall be amended or rescinded by the
Board of Directors of the Company, without your consent, to be consistent with
pooling-of-interests. accounting treatment for such transaction.

Notwithstanding the provisions of this Section 14, if, in connection with a
Change in Control, a tax under Section 4999 of the Internal Revenue Code would
be imposed on you (after taking into account the exceptions set forth in
Sections 280G(b)(4) and 280G(b)(5) of the Code), then the number of options
which shall become exercisable, realizable or vested as provided in such section
shall be reduced (or delayed), to the minimum extent necessary, so that no such
tax would be imposed on you.

Sincerely

/s/ Dennis M. Goett

Dennis M. Goett
Chief Financial Officer

I have carefully read the terms and conditions of the above and acknowledge and
accept the terms and conditions of this letter agreement.

Signature /s/ John Stopper
          ----------------

Date: 10.5.99