SEVERANCE PROTECTION AGREEMENT

Exhibit 10.3

SEVERANCE PROTECTION AGREEMENT

SEVERANCE PROTECTION AGREEMENT dated September 27, 2006, by and between ICF International, Inc., a Delaware corporation (the “Company”), and Alan Stewart (the “Executive”).

PURPOSE

The Board of Directors of the Company (the “Board”) recognizes that the possibility of a Change in Control (as hereinafter defined) of the Company exists and that the threat or occurrence of a Change in Control may result in the distraction of its key management personnel because of the uncertainties inherent in such a situation.

The Board has determined that it is essential and in the best interests of the Company and its stockholders to retain the services of the Executive in the event of the threat or occurrence of a Change in Control and to ensure the Executive’s continued dedication and efforts in such event without undue concern for the Executive’s personal financial and employment security.

In order to induce the Executive to remain in the employ of the Company, particularly in the event of the threat or occurrence of a Change in Control, the Company desires to enter into this Agreement to provide the Executive with certain benefits in the event the Executive’s employment is terminated as a result of, or in connection with, a Change in Control.

NOW, THEREFORE, in consideration of the respective agreements of the parties contained herein, it is agreed as follows:

SECTION 1. Definitions.

For purposes of this Agreement, the following terms have the meanings set forth below:

“Accrued Compensation” means an amount which includes all amounts earned or accrued by the Executive through and including the Termination Date but not paid to the Executive on or prior to such date, including (a) all base salary, (b) reimbursement for all reasonable expenses incurred by the Executive on behalf of the Company during the period ending on the Termination Date, (c) all vacation pay and (d) all bonuses and incentive compensation (other than the Pro Rata Bonus).

“Base Amount” means the Executive’s average annual taxable W-2 compensation during the three years (or such lesser period as the Executive has been employed by the Company) prior to the year in which the Termination Date occurs and includes all amounts of the Executive’s base salary that are deferred under any qualified or non-qualified employee benefit plan of the Company or any other agreement or arrangement.

“Beneficial Owner” has the meaning as used in Rule 13d-3 promulgated under the Securities Exchange Act. The terms “Beneficially Owned” and “Beneficial Ownership” each have a correlative meaning.

“Board” means the Board of Directors of the Company.

“Bonus Amount” means the annual bonus, if any, paid or payable to the Executive pursuant to any annual bonus or incentive plan maintained by the Company in respect of the fiscal year ending immediately prior to the fiscal year in which the Termination Date occurs. Bonus Amount includes only the short-term incentive portion of the annual bonus and does not include restricted stock awards, options or other long-term incentive compensation awarded to Executive.

“Cause” for the termination of the Executive’s employment with the Company shall mean any of the following: (a) any act that would constitute a material violation of the Company’s material written policies; (b) willfully engaging in conduct materially and demonstrably injurious to the Company, provided, however, that no act or failure to act, on the Executive’s part, shall be considered “willful” unless done, or omitted to be done, by the Executive not in good faith and without reasonable belief that his action or omission was in the best interest of the Company; (c) being indicted for, or if charged with but not indicted for, being tried for (i) a crime of embezzlement or a crime involving moral turpitude or (ii) a crime with respect to the Company involving a breach of trust or dishonesty or (iii) in either case, a plea of guilty or no contest to such a crime; or (d) abuse of alcohol in the workplace, use of any illegal drug in the workplace or a presence under the influence of alcohol or illegal drugs in the workplace.

“Change of Control” of the Company means, and shall be deemed to have occurred upon, any of the following events:

(a) The acquisition by any person (as defined in Section 3(a)(9) of the Exchange Act and used in Sections 13(d) and 14(d) thereof, including a group as defined in Section 13(d) thereof) (other than persons acting in concert as of August 31, 2006 who, as of such date, beneficially owned more than twenty percent (20%) or more of the securities entitled to vote generally in the election of directors of the Company), of beneficial ownership (as defined in Rule 13d-3 of the General Rules and Regulations under the Exchange Act) of securities representing thirty-five percent (35%) or more of the securities entitled to vote generally in the election of directors of the Company, provided, however, that the following acquisitions shall not constitute a Change in Control for purposes of this subparagraph (a): (i) any acquisition directly from the Company; (ii) any acquisition by the Company or any of its Subsidiaries; (iii) any acquisition by any employee benefit plan (or related trust) sponsored or maintained by the Company or any of its Subsidiaries; or (iv) any acquisition by any corporation pursuant to a transaction which complies with clauses (i), (ii) and (iii) of subparagraph (c) below; or

(b) Individuals who, as of August 31, 2006, constitute the Board (the “Incumbent Board”) cease for any reason to constitute at least a majority of the Board; provided, however, that any individual who becomes a director of the Company subsequent to August 31, 2006 and whose election, or whose nomination for election by the Company’s stockholders, to the Board

2

was either (i) approved by a vote of at least a majority of the directors then comprising the Incumbent Board or (ii) recommended by a nominating committee comprised entirely of directors who are then Incumbent Board members shall be considered as though such individual were a member of the Incumbent Board, but excluding, for this purpose, any such individual whose initial assumption of office occurs as a result of either an actual or threatened election contest (as such terms are used in Rule 14a-11 of Regulation 14A promulgated under the Exchange Act), other actual or threatened solicitation of proxies or consents or an actual or threatened tender offer; or

(c) Consummation of a reorganization, merger, or consolidation or sale or other disposition of all or substantially all of the assets of the Company (a “Business Combination”), in each case unless following such Business Combination, (i) all or substantially all of the persons who were the Beneficial Owners, respectively, of the outstanding shares and outstanding securities entitled to voted generally in the election of directors immediately prior to such Business Combination own, directly or indirectly, more than fifty percent (50%) of the combined voting power of the then outstanding securities entitled to vote generally in the election of directors of the Company, as the case may be, of the entity resulting from the Business Combination (including, without limitation, an entity which, as a result of such transaction, owns the Company or all or substantially all of the Company’s assets either directly or through one or more subsidiaries) in substantially the same proportions as their ownership, immediately prior to such Business Combination, of the outstanding securities entitled to vote generally in the election of directors (provided, however, that for purposes of this clause (i) any shares of common stock or such voting securities of such resulting entity received by such Beneficial Owners in such Business Combination other than as the result of such Beneficial Owners’ ownership of outstanding shares or such outstanding voting securities immediately prior to such Business Combination shall not be considered to be owned by such Beneficial Owners for the purposes of calculating their percentage of ownership of the outstanding common stock and voting power of the resulting entity); (ii) no person (excluding any entity resulting from such Business Combination or any employee benefit plan (or related trust) of the Company or such entity resulting from the Business Combination) beneficially owns, directly or indirectly, thirty-five percent (35%) or more of the combined voting power of the then outstanding securities entitled to vote generally in the election of directors of such entity resulting from the Business Combination unless such person owned thirty-five percent (35%) or more of the outstanding shares or outstanding securities entitled to vote generally in the election of directors immediately prior to the Business Combination; and (iii) at least a majority of the members of the Board of the entity resulting from such Business Combination were members of the Incumbent Board at the time of the execution of the initial agreement, or the action of the Board, providing for such Business Combination; or

(d) Approval by the Company’s stockholders of a complete liquidation or dissolution of the Company.

For purposes of clause (c), any person who acquires outstanding securities entitled to vote generally in the election of directors of the entity resulting from the Business Combination by virtue of ownership, prior to such Business Combination, of such voting securities of both the Company and the entity or entities with which the Company is combined shall be treated as two persons after the Business Combination, who shall be treated as owning such outstanding voting

3

securities of the entity resulting from the Business Combination by virtue of ownership, prior to such Business Combination of, respectively, such outstanding voting securities of the Company, and of the entity or entities with which the Company is combined.

“Code” means the Internal Revenue Code of 1986, as amended.

“Company” means ICF International, Inc., a Delaware corporation, and includes its Successors.

“Continuation Period” has the meaning set forth in Section 3.1(b)(iii).

“Disability” as used herein shall take its meaning from the definition set forth in any group long-term disability insurance contract maintained by the Company under which the Executive is covered, or, if the Company shall not maintain such insurance, “Disability” shall mean that the Executive is incapacitated by reason of a physical or mental illness which is long-term in nature and which prevents the Executive from performing the substantial and material duties of his employment with the Company, provided that such incapacity can reasonably be expected to prevent the Executive from working at least six consecutive months in any twelve month period. The Company may require the Executive to have an examination at any time for the purpose of determining whether the Executive has a long-term disability as described in the preceding sentence, and the Executive agrees to submit to such examination upon request of the Board of Directors, provided that the Company shall pay all costs and expenses associated with such examination.

“Full Release” means a written release, timely executed so that it is fully effective as of the date of payment pursuant to Section 3(b)(ii), in a form satisfactory to the Company (and similar to the Agreement set forth in Exhibit A), pursuant to which the Executive fully and completely releases the Company from all claims that the Executive may have against the Company (other than any claims that may arise or have arisen under this Agreement).

“Good Reason” means the occurrence after a Change in Control of any of the events or conditions described in clauses (a) through (f) hereof, without the Executive’s prior written consent:

(a) any (i) material adverse change in the Executive’s status, title, position or responsibilities (including reporting responsibilities) from the Executive’s status, title, position or responsibilities as in effect at any time within 180 days preceding the date of the Change in Control or at any time thereafter, (ii) assignment to the Executive of duties or responsibilities which are inconsistent with the Executive’s status, title, position or responsibilities as in effect at any time within 180 days preceding the date of the Change in Control or at any time thereafter, or (iii) in the case of an Executive who is an executive officer of the Company a significant portion of whose responsibilities relate to the Company’s status as a public company, the failure of such Executive to continue to serve as an executive officer of a public company, in each case except in connection with the termination of the Executive’s employment due to Disability, Cause, as a result of the Executive’s death or by the Executive other than for Good Reason;

4

(b) a reduction in Executive’s base salary or any failure to pay the Executive any cash compensation to which the Executive is entitled within fifteen (15) days after the date when due;

(c) the imposition of a requirement that the Executive be based (i) at any place outside a 50-mile radius from the Executive’s principal place of employment immediately prior to the Change in Control or (ii) at any location other than the Company’s corporate headquarters or, if applicable, the headquarters of the business unit by which he was employed immediately prior to the Change in Control, except, in each case, for reasonably required travel on Company business which is not materially greater in frequency or duration than prior to the Change in Control;

(d) the insolvency or the filing (by any party, including the Company) of a petition for bankruptcy with respect to the Company, which petition is not dismissed within 60 days;

(e) any material breach by the Company of any provision of this Agreement; or

(f) the failure of the Company to obtain, as contemplated in Section 7, an agreement, reasonably satisfactory to the Executive, from any Successor to assume and agree to perform this Agreement.

Notwithstanding anything to the contrary in this Agreement, no termination will be deemed to be for Good Reason hereunder if it results from an isolated, insubstantial and inadvertent action not taken by the Company in bad faith and which is remedied by the Company promptly after receipt of notice thereof given by the Executive.

“Notice of Termination” means a written notice from the Company or the Executive of the termination of the Executive’s employment which indicates the specific termination provision in this Agreement relied upon and which sets forth in reasonable detail the facts and circumstances claimed to provide a basis for termination of the Executive’s employment under the provision so indicated.

“Person” has the meaning as used in Section 13(d) or 14(d) of the Securities Exchange Act, and will include any “group” as such term is used in such sections.

“Pro Rata Bonus” means an amount equal to the Bonus Amount multiplied by a fraction, the numerator of which is the number of days elapsed in the then fiscal year through and including the Termination Date and the denominator of which is 365; provided that the provisions of this Agreement providing for the payment of a Pro Rata Bonus amount shall not be interpreted to call for the payment of amounts duplicative of amounts paid as part of the Base Amount.

“Securities Exchange Act” means the Securities Exchange Act of 1934, as amended.

“Subsidiary” means any corporation or entity with respect to which another specified corporation or entity has the power under ordinary circumstances to vote or direct the voting of sufficient securities to elect a majority of the directors or other managers.

5

“Successor” means a corporation or other entity acquiring all or substantially all the assets and business of the Company, whether by operation of law, by assignment or otherwise.

“Termination Date” means (a) in the case of the Executive’s death, the Executive’s date of death, (b) in the case of the termination of the Executive’s employment with the Company by the Executive for Good Reason, five days after the date the Notice of Termination is received by the Company, and (c) in all other cases, the date specified in the Notice of Termination; provided that if the Executive’s employment is terminated by the Company for Cause or due to Disability, the date specified in the Notice of Termination will be at least 30 days after the date the Notice of Termination is given to the Executive.

SECTION 2. Term of Agreement.

The term of this Agreement (the “Term”) will commence on the date hereof and will continue in effect until December 31, 2008; provided that on December 31, 2008 and each anniversary of such date thereafter, the Term shall automatically be extended for one additional year unless, not later than October 1 of such year, the Company or the Executive shall have given notice not to extend the Term; and further provided that, in the event a Change in Control occurs during the Term, the Term will be extended to the date 24 months after the date of the occurrence of such Change in Control.

SECTION 3. Termination of Employment.

3.1 If, during the Term, the Executive’s employment with the Company is terminated within 24 months following a Change in Control, the Executive will be entitled to the following compensation and benefits:

(a) If the Executive’s employment with the Company is terminated (i) by the Company for Cause or due to Disability, (ii) by reason of the Executive’s death or (iii) by the Executive other than for Good Reason, the Company will pay to the Executive or his designated beneficiary, as the case may be, his Accrued Compensation and, if such termination is other than by the Company for Cause, a Pro Rata Bonus.

(b) If the Executive’s employment with the Company is terminated for any reason other than as specified in Section 3.1(a), the Executive will be entitled to the following:

(i) the Company will pay the Executive all Accrued Compensation and a Pro Rata Bonus;

(ii) subject to the Executive providing the Company with a Full Release, the Company will pay the Executive as severance pay, and in lieu of any further compensation for periods subsequent to the Termination Date, in a single payment an amount in cash equal to three (3) times the Base Amount; provided, however, that if at the time of the Executive’s termination of employment, (i) the Executive is a specified employee within the meaning of Section 409A(a)(2)(B)(i) of the Code, (ii) the amount of the Executive’s severance pay exceeds the amount specified in Proposed Treasury

6

Regulation Section 1.409A-1(b)(9)(iii)(A) or any successor regulation thereto, or (iii) Section 409A is otherwise applicable to the Executive’s severance pay, then, and only in such event, such severance pay shall be paid in a single payment on the date that is six (6) months after the date of such termination.

(iii) subject to the Executive providing the Company with a Full Release and complying with his obligations under Section 6, the Company will, for a period of 36 months (the “Continuation Period”), at its expense provide to the Executive, the Executive’s dependents (as defined in the Company’s insurance contracts then in effect under which similarly situated executives are covered) and beneficiaries the same or equivalent life insurance, medical, dental, hospitalization, financial counseling and tax consulting benefits (the “Continuation Period Benefits”) provided to other similarly situated executives who continue in the employ of the Company during the Continuation Period (“similarly situated executives”) and their dependents and beneficiaries. The obligations of the Company to provide the Executive and the Executive’s dependents and beneficiaries with the Continuation Period Benefits shall not restrict or limit the Company’s right to terminate, amend or modify the benefits made available by the Company to its similarly situated executives or other employees, and following any such termination, amendment or modification, the Continuation Period Benefits that the Executive (and the Executive’s dependents and beneficiaries) shall be entitled to receive shall be so terminated, amended or modified. The Company’s obligations hereunder with respect to the foregoing benefits will be limited to the extent that the Executive obtains any such benefits pursuant to a subsequent employer’s benefit plans, in which case the Company may reduce the coverage of any benefits it is required to provide the Executive hereunder as long as the coverages and benefits of the combined benefit plans are no less favorable to the Executive than the coverages and benefits required to be provided hereunder. This