SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

June 18, 2013

Date of Report (Date of Earliest Event Reported)

FIRST POTOMAC REALTY TRUST

(Exact Name of Registrant as Specified in Its Charter)

7600 Wisconsin Avenue, 11^th Floor

Bethesda, Maryland 20814

(Address of Principal Executive Offices) (Zip Code)

(301) 986-9200

(Registrant’s Telephone Number, Including Area Code)

N/A

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

As previously disclosed in a Current Report on Form 8-K filed by First Potomac Realty Trust (the “Company”) on May 20, 2013, certain wholly owned subsidiaries (collectively, the “Sellers”) of First Potomac Realty Investment Limited Partnership, the operating partnership of the Company, entered into two separate contracts to sell a total of 24 industrial properties (comprising the majority of the Company’s industrial portfolio), consisting of an aggregate of approximately 4.3 million square feet. The aggregate sales price under the contracts for the 24 industrial properties is $259.0 million.

As previously disclosed, on May 7, 2013, the Company completed the sale of I-66 Commerce Center, a 236,000 square foot industrial property in Haymarket, Virginia, to Corporate Office Properties Trust for $17.5 million in cash.

On June 18, 2013, the Company completed the sale of the remainder of the portfolio to BRE/Industrial Acquisition Holdings 1, L.L.C., an affiliate of Blackstone Real Estate Partners VII (“Blackstone”), for $241.5 million in cash. Prior to the closing of the transaction, the Sellers and Blackstone entered into an amendment to the purchase and sale agreement in order to facilitate a potential future tax-free exchange under Section 1031 of the Internal Revenue Code with respect to $28.6 million related to two of the industrial properties sold to Blackstone.

The following are the 23 properties that were sold to Blackstone:

The Company received net proceeds of approximately $205 million from the sale of the 24 industrial properties after the repayment of $43.1 million of mortgage and other indebtedness secured by the properties, including prepayment penalties associated therewith, and the payment of customary closing costs. The Company intends to use the net proceeds from the sales primarily to repay outstanding indebtedness, including amounts outstanding under its unsecured revolving credit facility. For tax planning purposes, the Company also plans to place approximately $28 million of the net proceeds with a qualified intermediary in order to facilitate a potential 1031 exchange in the event the Company identifies an acquisition opportunity.

The foregoing description of the purchase and sale agreement (the “Sale Agreement”), dated as of May 17, 2013, by and among the Sellers and Blackstone is not complete and is subject to and qualified in its entirety by reference to the Sale Agreement, a copy of which was previously filed as Exhibit 10.1 to this Current Report on Form 8-K filed on May 20, 2013. A copy of the First Amendment to the Sale Agreement will be filed as an exhibit to the Company’s Quarterly Report on Form 10-Q for the quarter ending June 30, 2013.

In connection with the completion of the sale of the industrial properties, the Company is hereby filing, as Exhibit 99.1 hereto, an unaudited pro forma consolidated balance sheet of the Company as of March 31, 2013, and unaudited pro forma consolidated statements of operations for the three months ended March 31, 2013, and for each of the fiscal years ended December 31, 2012, 2011, and 2010. Exhibit 99.1 is hereby incorporated by reference herein.

On June 18, 2013, the Company issued a press release announcing the completion of the sale of the 23 industrial properties to Blackstone. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and shall not be deemed “filed” with the Securities and Exchange Commission (the “SEC”) for the purposes of Section 18 of the Securities Act of 1934, as amended (the “Exchange Act”), nor shall it be deemed incorporated by reference into any filing made by the Company under the Exchange Act or the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such a filing.

Cautionary Note Regarding Forward-Looking Statements

Statements in this Current Report on Form 8-K, and other statements that the Company may make, contain forward-looking statements, including, without limitation, statements regarding the use of proceeds from the sale of the Company’s industrial properties, within the meaning of the federal securities laws. Forward-looking statements, which are based on certain assumptions and describe future plans, strategies and expectations of the Company, are generally identifiable by use of the words “believe,” “expect,” “intend,” “anticipate,” “estimate,” “project” or similar expressions. The Company’s ability to predict results or the actual effect of future plans or strategies is inherently uncertain. Certain factors that could cause actual results to differ materially from the Company’s expectations include the risks detailed under “Risk Factors” in Part I, Item 1A in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012 and in the other documents the Company files with the SEC. Many of these factors are beyond the Company’s ability to control or predict. Forward-looking statements are not guarantees of performance. For forward-looking statements herein, the Company claims the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995. The Company assumes no obligation to update or supplement forward-looking statements that become untrue because of subsequent events. We have no duty to, and do not intend to, update or revise the forward-looking statements in this discussion after the date hereof, except as may be required by law. In light of these risks and uncertainties, you should keep in mind that any forward-looking statement made in this discussion, or elsewhere, might not occur.

(b) Pro forma financial information. The following pro forma financial information reflecting the transactions described above is filed as Exhibit 99.1 to this Current Report on Form 8-K.

(d) Exhibits. The following exhibits are being filed, or furnished, as applicable, with this Current Report on Form 8-K.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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