UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

Amendment No. 1

(Mark One)

for the quarterly period ended March 31, 2011

OR

for the transition period from              to             

Commission file number 001-34626

PIEDMONT OFFICE REALTY TRUST, INC.

(Exact name of registrant as specified in its charter)

11695 Johns Creek Parkway

Ste. 350

Johns Creek, Georgia 30097

(Address of principal executive offices)

(Zip Code)

(770) 418-8800

(Registrant’s telephone number, including area code)

N/A

(Former name, former address, and former fiscal year, if changed since last report)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer”, “accelerated filer”, and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

Number of shares outstanding of the Registrant’s

classes of common stock, as of May 4, 2011:

Class A Common Stock 172,749,781 shares

EXPLANATORY NOTE

The sole purpose of this Amendment No. 1 to Piedmont Office Realty Trust, Inc.’s (the “Registrant’s”) Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2011 is to furnish Exhibit 101 to the Form 10-Q in accordance with Rule 405 of Regulation S-T. Exhibit 101 consists of the following materials from the Registrant’s Form 10-Q for the quarterly period ended March 31, 2011, filed with the Securities and Exchange Commission on May 5, 2011, formatted in XBRL (eXtensible Business Reporting Language):

No other changes have been made to the Registrant’s Form 10-Q. This Amendment No. 1 does not reflect any subsequent events occurring after the original filing date of the Form 10-Q or modify or update in any way disclosures made in the original filing.

2

EXHIBIT INDEX

TO

FIRST QUARTER 2011

FORM 10-Q

OF

PIEDMONT OFFICE REALTY TRUST, INC.

3

4

SIGNATURES

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