WASHINGTON REAL ESTATE INVESTMENT TRUST UNDERWRITING AGREEMENT

Exhibit 1.1

Execution Copy

2,600,000 Common Shares of Beneficial Interest

WASHINGTON REAL ESTATE INVESTMENT TRUST

UNDERWRITING AGREEMENT

May 20, 2008

R AYMOND J AMES  & A SSOCIATES , I NC .

J.P. M ORGAN S ECURITIES I NC .

As Representatives of the Several Underwriters

c/o Raymond James & Associates, Inc.

880 Carillon Parkway

St. Petersburg, FL 33716

Dear Sirs:

1. Introductory . Washington Real Estate Investment Trust, a real estate investment trust organized under the laws of the State of Maryland (“ Company ”), agrees with the several Underwriters named in Schedule A hereto (the “ Underwriters ”) to issue and sell to the several Underwriters 2,600,000 of its common shares of beneficial interest (“ Firm Securities ”) and also proposes to issue and sell to the Underwriters, at the option of the Underwriters, an aggregate of not more than 390,000 additional common shares of beneficial interest (“ Optional Securities ”) as set forth below. The Firm Securities and the Optional Securities are herein collectively called the “ Offered Securities ”.

2. Representations and Warranties of the Company . The Company represents and warrants to, and agrees with, the several Underwriters that:

(a)  Filing and Effectiveness of Registration Statement . Certain terms are defined at the end of this subsection. The Company has filed with the Commission a registration statement on Form S-3 (No. 333-136921) covering the registration of the Offered Securities under the Act, including a related preliminary prospectus or prospectuses. At any particular time, this initial registration statement, in the form then on file with the Commission, including all material then incorporated by reference therein, all information contained in the registration statement (if any) pursuant to Rule 462(b) and then deemed to be a part of the initial registration statement, and all 430A Information and all 430C Information, that in any case has not then been superseded or modified, shall be referred to as the “ Initial Registration Statement ”. The Company may also have filed, or may file with the Commission, a Rule 462(b) registration statement covering the registration of Offered Securities. At any particular time, this Rule 462(b) registration statement, in the form then on file with the Commission, including the contents of the Initial Registration Statement incorporated by reference therein and including all 430A Information and all 430C Information, that in any case has not then been superseded or modified, shall be referred to as the “ Additional Registration Statement ”.

As of the time of execution and delivery of this Agreement, the Initial Registration Statement has been declared effective under the Act and is not proposed to be amended. Any Additional Registration Statement has or will become effective upon filing with the Commission pursuant to Rule 462(b) and is not proposed to be amended. The Offered Securities all have been or will be duly registered under the Act pursuant to the Initial Registration Statement and, if applicable, the Additional Registration Statement.

For purposes of this Agreement:

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

“ 430A Information ”, with respect to any registration statement, means information included in a prospectus and retroactively deemed to be a part of such registration statement pursuant to Rule 430A(b).

“ 430C Information ”, with respect to any registration statement, means information included in a prospectus then deemed to be a part of such registration statement pursuant to Rule 430C.

“ Act ” means the Securities Act of 1933, as amended.

“ Applicable Time ” means 10:00 a.m. (Eastern time) on the date of this Agreement.

“ Closing Date” has the meaning defined in Section 3 hereof.

“ Commission ” means the Securities and Exchange Commission.

“ Effective Date ” with respect to the Initial Registration Statement or the Additional Registration Statement (if any) means the date of the Effective Time thereof.

“ Effective Time ” with respect to the Initial Registration Statement or, if filed prior to the execution and delivery of this Agreement, the Additional Registration Statement means the date and time as of which such Registration Statement was declared effective by the Commission or has become effective upon filing pursuant to Rule 462(c). If an Additional Registration Statement has not been filed prior to the execution and delivery of this Agreement but the Company has advised the Representatives that it proposes to file one, “ Effective Time ” with respect to such Additional Registration Statement means the date and time as of which such Registration Statement is filed and becomes effective pursuant to Rule 462(b).

“ Exchange Act ” means the Securities Exchange Act of 1934.

“ Final Prospectus ” means the Statutory Prospectus that discloses the public offering price, other 430A Information and other final terms of the Offered Securities and otherwise satisfies Section 10(a) of the Act.

“ General Use Issuer Free Writing Prospectus ” means any Issuer Free Writing Prospectus that is intended for general distribution to prospective investors, as evidenced by its being so specified in Schedule B to this Agreement.

“ Issuer Free Writing Prospectus ” means any “issuer free writing prospectus,” as defined in Rule 433, relating to the Offered Securities in the form filed or required to be filed with the Commission or, if not required to be filed, in the form retained in the Company’s records pursuant to Rule 433(g).

“ Limited Use Issuer Free Writing Prospectus ” means any Issuer Free Writing Prospectus that is not a General Use Issuer Free Writing Prospectus.

A “ Registration Statement ” at any particular time means the Initial Registration Statement and any Additional Registration Statement as of such time. A “ Registration Statement ” without reference to a time means such Registration Statement as of its Effective Time. The Initial Registration Statement and the Additional Registration Statement are referred to collectively as the

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“ Registration Statements ” and individually as a “ Registration Statement ”. For purposes of the foregoing definitions, 430A Information with respect to a Registration Statement shall be considered to be included in such Registration Statement as of the time specified in Rule 430A.

“ Rules and Regulations ” means the rules and regulations of the Commission.

“ Statutory Prospectus ” as of any time means the prospectus included in a Registration Statement immediately prior to that time, including any document incorporated by reference therein and any 430A Information or 430C Information with respect to such Registration Statement. For purposes of the foregoing definition, 430A Information shall be considered to be included in the Statutory Prospectus as of the actual time that form of prospectus is filed with the Commission pursuant to Rule 424(b) or Rule 462(c) and not retroactively.

“ Trust Indenture Act ” means the Trust Indenture Act of 1939.

Unless otherwise specified, a reference to a “rule” is to the indicated rule under the Act.

(b)  Compliance with Securities Act Requirements . (i) On its respective Effective Date, on the date of this Agreement and on each Closing Date, each of the Initial Registration Statement and the Additional Registration Statement (if any) conformed and will conform in all material respects to the requirements of the Act and the Rules and Regulations and did not and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading, and (ii) on the date of this Agreement, and at the time of filing of the Final Prospectus pursuant to Rule 424(b) or (if no such filing is required) at the Effective Date of the Additional Registration Statement in which the Final Prospectus is included, the Final Prospectus will conform in all material respects to the requirements of the Act and the Rules and Regulations and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading. The preceding sentence does not apply to statements in or omissions from any such document based upon written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 8(b) hereof.

(c) Incorporated Documents . The documents incorporated or deemed to be incorporated by reference in the Registration Statement and the Prospectus, at the time they were or hereafter are filed with the Commission, complied and will comply in all material respects with the requirements of the 1934 Act and the Rules and Regulations.

(d) Ineligible Issuer Status . (i) At the time of initial filing of the Initial Registration Statement and (ii) at the date of this Agreement, the Company was not and is not an “ineligible issuer,” as defined in Rule 405, including (x) the Company or any other subsidiary in the preceding three years not having been convicted of a felony or misdemeanor or having been made the subject of a judicial or administrative decree or order as described in Rule 405 and (y) the Company in the preceding three years not having been the subject of a bankruptcy petition or insolvency or similar proceeding, not having had a registration statement be the subject of a proceeding under Section 8 of the Act and not being the subject of a proceeding under Section 8A of the Act in connection with the offering of the Offered Securities, all as described in Rule 405. At the time the Company or any person acting on its behalf (within the meaning, for this sentence only, of Rule 163(c)) made any offer in reliance on the exemption of Rule 163, the Company was a “well-known seasoned issuer” as defined in Rule 405, including not having been an “ineligible issuer” as defined in Rule 405.

(e) General Disclosure Package . As of the Applicable Time, neither (i) the General Use Issuer Free Writing Prospectus(es) issued at or prior to the Applicable Time, the preliminary prospectus, dated May 19, 2008 (which is the most recent Statutory Prospectus distributed to

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investors generally) and the other information, if any, stated in Schedule B to this Agreement to be included in the General Disclosure Package, all considered together (collectively, the “ General Disclosure Package ”), nor (ii) any individual Limited Use Issuer Free Writing Prospectus, when considered together with the General Disclosure Package, included any untrue statement of a material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any Statutory Prospectus or any Issuer Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 8(b) hereof.

(f) Issuer Free Writing Prospectuses . Each Issuer Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Offered Securities or until any earlier date that the Company notified or notifies the Representatives as described in the next sentence, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information then contained in the Registration Statement. If at any time following issuance of an Issuer Free Writing Prospectus there occurred or occurs an event or development as a result of which such Issuer Free Writing Prospectus conflicted or would conflict with the information then contained in the Registration Statement or included or would include an untrue statement of a material fact or omitted or would omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances prevailing at that subsequent time, not misleading, (i) the Company has promptly notified or will promptly notify the Representatives and (ii) the Company has promptly amended or will promptly amend or supplement such Issuer Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission.

(g) Good Standing of the Company . The Company has been duly organized and is validly existing as a real estate investment trust of unlimited duration with transferable shares of beneficial interest in good standing under the laws of the State of Maryland, with full power and authority to own, lease and operate its properties and to conduct its business as described in the General Disclosure Package and to enter into this Agreement and to consummate the transactions contemplated hereby. The Company is duly qualified to transact business and is in good standing in each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except where the failure to so qualify or be in good standing would not result in a material adverse change in the condition, financial or otherwise, or the results of operations, business, properties or prospects of the Company and its subsidiaries considered as one enterprise, whether or not arising in the ordinary course of business (a “ Material Adverse Effect ”).

(h) Subsidiaries . Each “significant subsidiary” of the Company (as such term is defined in Rule 1-02 of Regulation S-X promulgated under the 1933 Act) (each, a “ Subsidiary ” and, collectively, the “ Subsidiaries ”) (which term includes corporations, limited and general partnerships, limited liability companies, joint ventures and other entities, and includes direct and indirect subsidiaries), if any, has been duly organized and is validly existing as a corporation, limited liability company or partnership, as the case may be, in good standing under the laws of the jurisdiction of its incorporation or organization, has power and authority to own, lease and operate its properties and to conduct its business as described in the General Disclosure Package and is duly qualified to transact business and is in good standing in each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except where the failure to so qualify or be in good standing would not result in a Material Adverse Effect. Except as otherwise stated in the General Disclosure Package, all of the issued and outstanding capital stock or other ownership interests of each Subsidiary have been duly authorized and validly issued, are fully paid and non-assessable and are owned by the

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Company, directly or through subsidiaries, free and clear of any security interest, mortgage, pledge, lien, encumbrance, claim or equity; and none of the outstanding shares of capital stock of any Subsidiary was issued in violation of preemptive or other similar rights of any security holder of such Subsidiary.

(i) Offered Securities . The Offered Securities and all other outstanding shares of beneficial interest of the Company have been duly authorized; the authorized equity capitalization of the Company is as set forth in the General Disclosure Package; all outstanding shares of beneficial interest of the Company are, and, when the Offered Securities have been delivered and paid for in accordance with this Agreement on each Closing Date, such Offered Securities will have been, validly issued, fully paid and nonassessable, will be consistent with the information in the General Disclosure Package and will conform to the description thereof contained in the Final Prospectus; the shareholders of the Company have no preemptive rights with respect to the Offered Securities; and none of the outstanding shares of beneficial interest of the Company have been issued in violation of any preemptive or similar rights of any security holder.

(j) Finder’s Fee . Except as disclosed in the General Disclosure Package, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or any Underwriter for a brokerage commission, finder’s fee or other like payment in connection with this offering.

(k) Registration Rights . Except as disclosed in the General Disclosure Package, there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to a Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act (collectively, “ registration rights ”), and any person to whom the Company has granted registration rights has agreed not to exercise such rights until after the expiration of the Lock-Up Period referred to in Section 5 hereof.

(l) Listing . As of the First Closing Date, the Offered Securities will have been approved for listing on the New York Stock Exchange, subject to notice of issuance.

(m) Absence of Further Requirements . No consent, approval, authorization, or order of, or filing or registration with, any person (including any governmental agency or body or any court) is required for the consummation by the Company of the transactions contemplated by this Agreement in connection with the offering, issuance and sale of the Offered Securities by the Company, except such as have been obtained, or made and such as may be required under state securities laws.

(n) Title to Property . The Company and its subsidiaries have good and marketable title to, or valid and enforceable leasehold estates in, all items of real and personal property referred to in the General Disclosure Package as owned or leased by them, in each case free and clear of all liens, encumbrances, claims, security interests and defects, other than those referred to in the General Disclosure Package or that are not material in amount. The Company has no reason to believe that the lessee under any lease (excluding leases for which rent payments due for the remainder of such lease are less than $1,000,000) calling for annual lease payments in excess of $1,000,000 is not financially capable of performing its obligations thereunder.

(o) Absence of Defaults and Conflicts Resulting from Transaction . The execution, delivery and performance of this Agreement, and the issuance and sale of the Offered Securities will not result in a breach or violation of any of the terms and provisions of, or constitute a default or a

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Debt Repayment Triggering Event (as defined below) under, or result in the imposition of any lien, charge or encumbrance upon any property or assets of the Company or any of its subsidiaries pursuant to, the declaration of trust, partnership agreement, charter or by-laws or other organizational documents of the Company or any of its subsidiaries, any statute, rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any of its subsidiaries or any of their properties, or any agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the properties of the Company or any of its subsidiaries is subject; a “ Debt Repayment Triggering Event ” means any event or condition that gives, or with the giving of notice or lapse of time would give, the holder of any note, debenture, or other evidence of indebtedness (or any person acting on such holder’s behalf) the right to require the repurchase, redemption or repayment of all or a portion of such indebtedness by the Company or any of its subsidiaries.

(p) Absence of Existing Defaults and Conflicts . Neither the Company nor any of its subsidiaries is in violation of its respective declaration of trust, partnership agreement, charter or by-laws or other organizational document or in default (or with the giving of notice or lapse of time would be in default) under any existing obligation, agreement, covenant or condition contained in any indenture, loan agreement, mortgage, lease or other agreement or instrument to which any of them is a party or by which any of them is bound or to which any of the properties of any of them is subject, except such defaults that would not, individually or in the aggregate, result in a Material Adverse Effect.

(q) Authorization of Agreement . This Agreement has been duly authorized, executed and delivered by the Company.

(r) Possession of Licenses and Permits . The Company and its subsidiaries possess, and are in compliance with the terms of, all certificates, authorizations, franchises, licenses and permits (“ Licenses ”) necessary or material to the conduct of the business now conducted or proposed in the General Disclosure Package to be conducted by them and have not received any notice of proceedings relating to the revocation or modification of any Licenses that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(s) Absence of Labor Dispute . No labor dispute with the employees of the Company or any of its subsidiaries exists or, to the knowledge of the Company, is imminent, and the Company is not aware of any existing or imminent labor disturbance by the employees of any of its or its subsidiaries’ principal suppliers, contractors or customers, that, in any such case, could have a Material Adverse Effect.

(t) Possession of Intellectual Property . The Company and its subsidiaries own, possess or can acquire on reasonable terms, adequate trademarks, trade names and other rights to inventions, know-how, patents, copyrights, confidential information and other intellectual property (collectively, “ intellectual property rights ”) necessary to conduct the business now operated by them, or presently employed by them, and have not received any notice of infringement of or conflict with asserted rights of others with respect to any intellectual property rights that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(u)  Environmental Laws . Except as disclosed in the General Disclosure Package, neither the Company nor any of its subsidiaries is in violation of any statute, any rule, regulation, decision or order of any governmental agency or body or any court, domestic or foreign, relating to the use, disposal or release of hazardous or toxic substances or relating to the protection or restoration of the environment or human exposure to hazardous or toxic substances (collectively,

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“ environmental laws ”), owns or operates any real property contaminated with any substance that is subject to any environmental laws, is liable for any off-site disposal or contamination pursuant to any environmental laws, or is subject to any claim relating to any environmental laws, which violation, contamination, liability or claim would individually or in the aggregate have a Material Adverse Effect; and the Company is not aware of any pending investigation which might lead to such a claim.

(v) Accurate Disclosure . The statements in the General Disclosure Package and the Final Prospectus under the heading “Description of Shares” and under the heading “Risk Factors” in the Company’s 2007 Annual Report on Form 10-K and the statements in the Registration Statement under Item 15 insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, are accurate and fair summaries of such legal matters, agreements, documents or proceedings and present the information required to be shown in all material respects.

(w) REIT Status . With respect to all tax periods regarding which the Internal Revenue Service is or will be entitled to assert any claim, the Company has met the requirements for qualification as a real estate investment trust under Sections 856 through 860 of the Internal Revenue Code, as amended, and the Company’s present and contemplated operations, assets and income continue to meet such requirements.

(x) Insurance . The Company and its subsidiaries are insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are prudent and customary in the businesses in which they are engaged; the Company has no reason to believe that it or any of its subsidiaries will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage from similar insurers as may be necessary to continue its business at a cost that would not have a Material Adverse Effect; and the Company and each of its subsidiaries has obtained title insurance on all of the properties owned by each of them in an amount at least equal to the original purchase price to acquire land and improvements and such title insurance is in full force and effect.

(y) Taxes . The Company has filed all federal, state and foreign income tax returns that have been required to be filed and has paid all taxes indicated by said returns and all assessments received by it to the extent that such taxes have become due.

(z) Statistical and Market-Related Data . Any third-party statistical and market-related data included or incorporated by reference in a Registration Statement or a Statutory Prospectus are based on or derived from sources that the Company believes to be reliable and accurate.

(aa) Compliance with the Sarbanes-Oxley Act . Except as set forth in the General Disclosure Package, (i) the Company, its subsidiaries and the Company’s Board of Trustees (the “ Board ”) are in compliance in all material respects with Sarbanes-Oxley (as defined below) and all applicable Exchange Rules (as defined below); (ii) the Company has adopted and has or, upon consummation of the offering of the Offered Securities, will have disclosed corporate governance guidelines; (iii) the Company maintains a system of internal controls, including, but not limited to, disclosure controls and procedures, internal control over financial reporting, an internal audit function and legal and regulatory compliance controls (collectively, “ Internal Controls ”), which complies with the Securities Laws (as defined below) and is or, upon consummation of the offering of the Offered Securities will be overseen by the Audit Committee (the “ Audit Committee ”) of the Board in accordance with Exchange Rules; (iv) the Company has not publicly disclosed or reported to the Audit Committee or the Board, and within the next 90 days the Company does not reasonably expect to publicly disclose or report to the Audit Committee or the Board, a significant deficiency, material weakness, change in Internal Controls or fraud involving management or other employees who have a significant role in Internal Controls (each, an

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“ Internal Control Event ”), any violation of, or failure to comply with, the Securities Laws, or any matter which, if determined adversely, would have a Material Adverse Effect; and (v) “ Securities Laws ” means, collectively, the Sarbanes-Oxley Act of 2002 (“ Sarbanes-Oxley ”), the Act, the Exchange Act, the Rules and Regulations, the auditing principles, rules, standards and practices applicable to auditors of “issuers” (as defined in Sarbanes-Oxley) promulgated or approved by the Public Company Accounting Oversight Board (“ PCAOB Rules ” and “ PCAOB ,” respectively), and, as applicable, the rules of the New York Stock Exchange (“ Exchange Rules ”).

(bb) Litigation . Except as disclosed in the General Disclosure Package, there are no pending actions, suits or proceedings (including any inquiries or investigations by any court or governmental agency or body, domestic or foreign) against or affecting the Company, any of its subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under this Agreement, or which are otherwise material in the context of the sale of the Offered Securities; and no such actions, suits or proceedings (including any inquiries or investigations by any court or governmental agency or body, domestic or foreign) are threatened or, to the Company’s knowledge, contemplated.

(cc) Financial Statements and Independent Accountants . The financial statements included in each Registration Statement and the General Disclosure Package present fairly the financial position of the Company and its consolidated subsidiaries as of the dates shown and their results of operations and cash flows for the periods shown, and such financial statements have been prepared in conformity with the generally accepted accounting principles in the United States (“ GAAP ”) applied on a consistent basis and the schedules included in each Registration Statement present fairly the information required to be stated therein; and the assumptions used in preparing the pro forma financial statements included in each Registration Statement and the General Disclosure Package provide a reasonable basis for presenting the significant effects directly attributable to the transactions or events described therein, the related pro forma adjustments give appropriate effect to those assumptions, and the pro forma columns therein reflect the proper application of those adjustments to the corresponding historical financial statement amounts. The supporting schedules, if any, included in the Registration Statement and the General Disclosure Package present fairly in accordance with GAAP the information required to be stated therein. The selected financial data included in the General Disclosure Package present fairly the information shown therein and have been compiled on a basis consistent with that of the audited financial statements included in the Registration Statement and the General Disclosure Package. The historical summaries of revenue and certain operating expenses included in the Registration Statement and the General Disclosure Package present fairly the revenue and those operating expenses included in such summaries of the properties related thereto for the periods specified in conformity with GAAP. The accountants who certified the financial statements and any supporting schedules thereto included in each Registration Statement and the General Disclosure Package are independent public accountants within the meaning of the Securities Laws.

(dd) Accuracy of Exhibits . There are no contracts or documents that are required to be described in the Registration Statement, the Prospectus or the documents incorporated by reference therein or to be filed as exhibits thereto that have not been so described and filed as required.

(ee) No Material Adverse Change in Business . Except as disclosed in the General Disclosure Package, since the end of the period covered by the latest audited financial statements included in the General Disclosure Package (i) there has been no change, nor any development or event involving a prospective change, in the condition (financial or otherwise), results of operations, business, properties or prospects of the Company and its subsidiaries, taken as a whole that is material and adverse, (ii) except as disclosed in or contemplated by the General Disclosure

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Package, there has been no dividend or distribution of any kind declared, paid or made by the Company on any class of its capital stock and (iii) except as disclosed in or contemplated by the General Disclosure Package, there has been no material adverse change in the capital stock, short-term indebtedness, long-term indebtedness, net current assets or net assets of the Company and its subsidiaries.

(ff) Investment Company Act . The Company is not and, after giving effect to the offering and sale of the Offered Securities and the application of the proceeds thereof as described in the General Disclosure Package, will not be an “investment company” as defined in the Investment Company Act of 1940 (the “ Investment Company Act ”).

(gg) Ratings . No “nationally recognized statistical rating organization” as such term is defined for purposes of Rule 436(g)(2) (i) has imposed (or has informed the Company that it is considering imposing) any condition (financial or otherwise) on the Company’s retaining any rating assigned to the Company or any securities of the Company or (ii) has indicated to the Company that it is considering any of the actions described in Section 7(c)(ii) hereof.

3. Purchase, Sale and Delivery of Offered Securities . On the basis of the representations, warranties and agreements and subject to the terms and conditions set forth herein, the Company agrees to sell to the several Underwriters, and each of the Underwriters agrees, severally and not jointly, to purchase from the Company, at a purchase price of $33.408 per share, the respective number of Firm Securities set forth opposite the names of the Underwriters set forth in Schedule A hereto.

The Company will deliver the Firm Securities to or as instructed by the Representatives for the accounts of the several Underwriters in a form reasonably acceptable to the Representatives against payment of the purchase price by the Underwriters in Federal (same day) funds by wire transfer to an account at a bank acceptable to the Representatives drawn to the order of Washington Real Estate Investment Trust at the office of Vinson & Elkins LLP, 1455 Pennsylvania Avenue, Washington, DC, 20004, at 10:00 A.M., New York time, on May 23, 2008, or at such other time not later than seven full business days thereafter as the Representatives and the Company determine, such time being herein referred to as the “ First Closing Date ”. For purposes of Rule 15c6-1 under the Securities Exchange Act of 1934, the First Closing Date (if later than the otherwise applicable settlement date) shall be the settlement date for payment of funds and delivery of securities for all the Offered Securities sold pursuant to the offering. The Firm Securities so to be delivered or evidence of their issuance will be made available for checking at the above office of Vinson & Elkins LLP at least 24 hours prior to the First Closing Date.

In addition, upon written notice from the Representatives given to the Company from time to time not more than 30 days subsequent to the date of the Final Prospectus, the Underwriters may purchase all or less than all of the Optional Securities at the purchase price per Security to be paid for the Firm Securities less an amount equal to any dividend paid by the Company and payable on any Firm Securities and not payable on such Optional Securities. The Company agrees to sell to the Underwriters the number of Optional Securities specified in such notice and the Underwriters agree, severally and not jointly, to purchase such Optional Securities. Such Optional Securities shall be purchased for the account of each Underwriter in the same proportion as the number of Firm Securities set forth opposite such Underwriter’s name bears to the total number of Firm Securities (subject to adjustment by the Representatives to eliminate fractions) and may be purchased by the Underwriters only for the purpose of covering over-allotments made in connection with the sale of the Firm Securities. No Optional Securities shall be sold or delivered unless the Firm Securities previously have been, or simultaneously are, sold and delivered. The right to purchase the Optional Securities or any portion thereof may be exercised from time to time and to the extent not previously exercised may be surrendered and terminated at any time upon notice by the Representatives to the Company.

Each time for the delivery of and payment for the Optional Securities, being herein referred to as an “ Optional Closing Date ”, which may be the First Closing Date (the First Closing Date and each

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Optional Closing Date, if any, being sometimes referred to as a “ Closing Date ”), shall be determined by the Representatives but shall be not later than five full business days after written notice of election to purchase Optional Securities is given. The Company will deliver the Optional Securities being purchased on each Optional Closing Date to or as instructed by the Representatives for the accounts of the several Underwriters in a form reasonably acceptable to the Representatives against payment of the purchase price therefor in Federal (same day) funds by wire transfer to an account at a bank acceptable to the Representatives drawn to the order of Washington Real Estate Investment Trust, at the above office of Vinson & Elkins LLP. The Optional Securities being purchased on each Optional Closing Date or evidence of their issuance will be made available for checking at the above office of Vinson & Elkins LLP at a reasonable time in advance of such Optional Closing Date.

4. Offering by Underwriters . It is understood that the several Underwriters propose to offer the Offered Securities for sale to the public as set forth in the Final Prospectus.

5. Certain Agreements of the Company . The Company agrees with the several Underwriters that:

(a)  Additional Filings . Unless filed pursuant to Rule 462(c) as part of the Additional Registration Statement in accordance with the next sentence, the Company will file the Final Prospectus, in a form approved by the Representatives, with the Commission pursuant to and in accordance with subparagraph (1) (or, if applicable and if consented to by the Representatives, subparagraph (4)) of Rule 424(b) not later than the earlier of (A) the second business day following the execution and delivery of this Agreement or (B) the fifteenth business day after the Effective Date of the Initial Registration Statement. The Company will advise the Representatives promptly of any such filing pursuant to Rule 424(b) and provide satisfactory evidence to the Representatives of such timely filing. If an Additional Registration Statement is necessary to register a portion of the Offered Securities under the Act but the Effective Time thereof has not occurred as of the execution and delivery of this Agreement, the Company will file the additional registration statement or, if filed, will file a post-effective amendment thereto with the Commission pursuant to and in accordance with Rule 462(b) on or prior to 10:00 P.M., New York time, on the date of this Agreement or, if earlier, on or prior to the time the Final Prospectus is finalized and distributed to any Underwriter, or will make such filing at such later date as shall have been consented to by the Representatives.

(b)  Filing of Amendments; Response to Commission Requests . The Company will promptly advise the Representatives of any proposal to amend or supplement at any time the Initial Registration Statement, any Additional Registration Statement or any Statutory Prospectus and will not effect such amendment or supplementation without the Representatives’ consent; and the Company will also advise the Representatives promptly of (i) the effectiveness of any Additional Registration Statement (if its Effective Time is subsequent to the execution and delivery of this Agreement), (ii) any amendment or supplementation of a Registration Statement or any Statutory Prospectus, (iii) any request by the Commission or its staff for any amendment to any Registration Statement, for any supplement to any Statutory Prospectus or for any additional information, (iv) the institution by the Commission of any stop order proceedings in respect of a Registration Statement or the threatening of any proceeding for that purpo