UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 7, 2010

Mirant Corporation

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (678) 579-5000

N/A

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

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

Section 2 – Financial Information

On May 7, 2010, Mirant Corporation (the “Company,” “Mirant,” “we,” “us,” or “our”) issued a press release announcing its financial results for the quarter ended March 31, 2010. A copy of Mirant’s May 7, 2010, press release is furnished hereto as Exhibit 99.1 and incorporated by reference herein. The press release contains certain forward-looking statements, all of which are subject to the cautionary statement about forward-looking statements set forth therein. Except as otherwise provided in the press release, the press release speaks only as of the date of such press release and it shall not create any implication that the affairs of Mirant will have continued unchanged since such date.

We use certain non-GAAP financial measures in the press release and on our earnings conference calls. These non-GAAP financial measures include adjusted net income, adjusted EBITDA, realized and unrealized gross margins, adjusted gross margin, adjusted operations and maintenance expenses, adjusted net cash provided by operating activities, adjusted free cash flow and adjusted free cash flow (without MD HAA). The definitions of these non-GAAP financial measures, together with a discussion of the usefulness and purpose of such measures, is provided in the explanations attached hereto as Exhibit 99.2. Reconciliations of each of these non-GAAP measures to the most directly comparable GAAP measure can be found either in our earnings press release or in the investor presentation that we intend to utilize on our earnings conference call, which will be posted on our website prior to the commencement of the conference call.

The information contained in Item 2.02 in this Current Report on Form 8-K is to be considered “furnished” pursuant to Item 2.02 of Form 8-K and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, nor shall it be deemed incorporated by reference in any Mirant filing or report with the Securities and Exchange Commission, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such a filing or report.

Section 9 – Financial Statements and Exhibits

(d) Exhibits.

Additional Information and Where To Find It

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. In connection with the proposed merger between RRI Energy and Mirant, RRI Energy will file with the SEC a Registration Statement on Form S-4 that will include a joint proxy statement of RRI Energy and Mirant that also constitutes a prospectus of RRI Energy. RRI Energy and Mirant will mail the joint proxy statement/prospectus to their respective shareholders. RRI Energy and Mirant urge investors and shareholders to read the joint proxy statement/prospectus regarding the proposed merger when it becomes available, as well as other documents filed with the SEC, because they will contain important information. You may obtain copies of all documents filed with the SEC regarding this transaction, free of charge, at the SEC’s website (www.sec.gov). You may also obtain these documents, free of charge, from RRI Energy’s website (www.rrienergy.com) under the tab “Investor Relations” and then under the heading “Company Filings.” You may also obtain these documents, free of charge, from Mirant’s website (www.mirant.com) under the tab “Investor Relations” and then under the heading “SEC Filings.”

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Participants in The Merger Solicitation

RRI Energy, Mirant, and their respective directors, executive officers and certain other members of management and employees may be soliciting proxies from RRI Energy and Mirant shareholders in favor of the merger and related matters. Information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of RRI Energy and Mirant shareholders in connection with the proposed merger will be set forth in the joint proxy statement/prospectus when it is filed with the SEC. You can find information about RRI Energy’s executive officers and directors in its definitive proxy statement filed with the SEC on April 1, 2010. You can find information about Mirant’s executive officers and directors in its definitive proxy statement filed with the SEC on March 26, 2010 and supplemented on April 28, 2010. Additional information about RRI Energy’s executive officers and directors and Mirant’s executive officers and directors can be found in the above-referenced Registration Statement on Form S-4 when it becomes available. You can obtain free copies of these documents from RRI Energy and Mirant using the contact information above.

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SIGNATURES

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.

Date: May 7, 2010

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