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): November 15, 2012

Patriot Coal Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (314) 275-3600

Not Applicable

(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):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01. Entry into a Material Definitive Agreement

On November 15, 2012, Patriot Coal Corporation (“Patriot”) and Ohio Valley Environmental Coalition, Inc., West Virginia Highlands Conservancy, Inc. and Sierra Club (collectively, the “Plaintiffs”) entered into an agreement (the “Settlement Agreement”) pursuant to which the parties agreed to extend the deadlines by which certain Patriot subsidiaries must install selenium treatment technology at select outfalls that are the subject of lawsuits previously brought by the Plaintiffs against Patriot and certain of its subsidiaries. Pursuant to the Settlement Agreement, the parties committed to jointly petition the U.S. District Court for the Southern District of West Virginia (the “U.S. District Court”) to extend by twelve months the compliance schedules for each category of outlets included under the comprehensive consent decree (the “Consent Decree”) entered by the U.S. District Court in March 2012 in settlement of a lawsuit filed by the Plaintiffs during February 2011. In addition, the parties agreed to request the U.S. District Court to extend until August 1, 2014 the compliance deadline for Hobet Mining, LLC (“Hobet”) to achieve compliance with selenium limitations pursuant to an October 8, 2010 order issued in connection with an October 2009 lawsuit filed by the Plaintiffs.

Under the terms of the Settlement Agreement, Patriot and the Plaintiffs agreed to the following:

Also on November 15, 2012, Patriot, along with its subsidiaries Apogee Coal Company, LLC, Catenary Coal Company, LLC and Hobet, and the Plaintiffs lodged a proposed modification to the Consent Decree (the “Modified Consent Decree”) in the U.S. District Court reflecting the terms of the Settlement Agreement that are relevant to the Consent Decree.

The Settlement Agreement and Modified Consent Decree must be approved by the U.S. Bankruptcy Court for the Southern District of New York before they become effective. In addition, the effectiveness of the Settlement Agreement is contingent upon the U.S. District Court modifying the Consent Decree and October 8, 2010 Order in accordance with the Settlement Agreement, and is also subject to a public comment period.

This description is a summary and does not purport to be a complete description of the Settlement Agreement or the Modified Consent Decree. It is qualified in its entirety by reference to the Settlement Agreement and the Modified Consent Decree, which are attached hereto as Exhibit 10.1 and Exhibit 10.2, respectively, and incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

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.

Dated: November 20, 2012

EXHIBIT INDEX