Exhibit 5.1 [Hogan Lovells US LLP Letterhead] July 1, 2011 Board of Trustees

First Potomac Realty Trust

7600 Wisconsin Avenue

Bethesda, MD 20814 Ladies and Gentlemen: We are acting as counsel to First Potomac Realty Trust, a Maryland real estate investment trust (the Company),
in connection with its registration statement on Form S-8 (the Registration Statement), filed with the Securities and
Exchange Commission under the Securities Act of 1933, as amended, relating to the proposed offering of up to 4,500,000
newly issued common shares of beneficial interest, par value $0.001 per share, of the Company (the Shares), all of
which Shares are issuable pursuant to the Companys 2009 Equity Compensation Plan, as amended (the Plan). This
opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of
Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement. For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we
have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the
aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the
accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the
conformity to authentic original documents of all documents submitted to us as copies (including telecopies). We also
have assumed that the Shares will not be issued in violation of the ownership limit contained in the Companys First
Amended and Restated Declaration of Trust. As to all matters of fact, we have relied on the representations and
statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on.
This opinion letter is given, and all statements herein are made, in the context of the foregoing. This opinion letter is based as to matters of law solely on the applicable provisions of Title 8 of the
Corporations and Associations Article of the Annotated Code of Maryland, as amended, and applicable provisions of the
Maryland General Corporation Law, as amended. We express no opinion herein as to any other laws, statutes, ordinances,
rules, or regulations. As used herein, the terms Title 8 of the Corporations and Associations Article of the Annotated
Code of Maryland, as amended and Maryland General Corporation Law, as amended include the applicable statutory
provisions contained therein, all applicable provisions of the Maryland Constitution and reported judicial decisions
interpreting these laws.  1




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Board of Trustees

First Potomac Realty Trust

July 1, 2011

Page 2 Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) effectiveness of the
Registration Statement, (ii) issuance of the Shares pursuant to the terms of the Plan, and (iii) receipt by the Company
of the consideration for the Shares specified in the applicable resolutions of the Board of Trustees and in the Plan,
the Shares will be validly issued, fully paid and nonassessable. This opinion letter has been prepared for use in connection with the Registration Statement. We assume no
obligation to advise you of any changes in the foregoing subsequent to the effective date of the Registration
Statement. We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement. In giving
this consent, we do not thereby admit that we are an expert within the meaning of the Securities Act of 1933, as
amended. Very truly yours,/s/ Hogan Lovells US LLPHogan Lovells US LLP
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