UNITED STATES

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

Date of Report (date of earliest event reported): January 28, 2016

CENTERPOINT ENERGY, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (713) 207-1111

(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):

Purchase Agreement

On January 28, 2016, CenterPoint Energy, Inc. (the “Company”) entered into a Purchase Agreement (the “Purchase Agreement”) with Enable Midstream Partners, LP (the “Partnership”) pursuant to which it agreed to purchase in a private placement (the “Private Placement”) an aggregate of 14,520,000 10% Series A Fixed-to-Floating Non-Cumulative Redeemable Perpetual Preferred Units representing limited partner interests in the Partnership (the “Series A Preferred Units”) for a cash purchase price of $25.00 per Series A Preferred Unit (the “Issue Price”). The closing of the Private Placement, which is expected to occur prior to the end of the first quarter of 2016, is subject to the completion of due diligence by the Company, including the review of the Partnership’s audited financial statements and Form 10-K for the year ended December 31, 2015, and certain customary closing conditions. In connection with the Private Placement, the Partnership will redeem approximately $363,000,000 of notes scheduled to mature in 2017 payable to a wholly-owned subsidiary of the Company. The Company will use the proceeds from this redemption for its investment in the Series A Preferred Units pursuant to the Purchase Agreement.

The Purchase Agreement contains customary representations, warranties and covenants of the Partnership and the Company. The Partnership, on the one hand, and the Company, on the other hand, have agreed to indemnify each other and their respective officers, directors, managers, employees, agents, counsel, accountants, investment bankers and other representatives against certain losses resulting from breaches of their respective representations, warranties and covenants, subject to certain negotiated limitations and survival periods set forth in the Purchase Agreement.

Pursuant to the Purchase Agreement, in connection with the closing of the Private Placement, Enable GP, LLC, the general partner of the Partnership (the “General Partner”) will execute a Third Amended and Restated Agreement of Limited Partnership of the Partnership (the “Amended Partnership Agreement”) to, among other things, authorize and establish the terms of the Series A Preferred Units and the other series of preferred units that are issuable upon conversion of the Series A Preferred Units, in the form attached as an exhibit to the Purchase Agreement. Also, the Partnership has agreed to enter into a registration rights agreement with the Company at the closing of the Private Placement, pursuant to which, among other things, the Partnership will give the Company certain rights to require the Partnership to file and maintain a registration statement with respect to the resale of the Series A Preferred Units and any other series of preferred units or common units representing limited partnership interests in the Partnership that are issuable upon conversion of the Series A Preferred Units.

The Series A Preferred Units will rank senior to the Partnership’s common units with respect to the payment of distributions and distribution of assets upon liquidation, dissolution and winding up. The Series A Preferred Units have no stated maturity and are not subject to any sinking fund and will remain outstanding indefinitely unless repurchased or redeemed by the Partnership or converted into its common units in connection with a change of control.

Holders of the Series A Preferred Units will receive, on a non-cumulative basis and if and when declared by the General Partner, a quarterly cash distribution, subject to certain adjustments, equal to (x) from the date of original issue to, but not including, the five year anniversary of the original issue date, an annual rate of 10% on the stated liquidation preference and (y) thereafter, an annual rate of LIBOR plus a spread of 850 bps on the stated liquidation preference.

At any time on or after five years after the original issue date, the Partnership may redeem the Series A Preferred Units, in whole or in part, from any source of funds legally available for such purpose, by paying $25.50 per unit plus an amount equal to all accumulated and unpaid distributions thereon to the date of redemption, whether or not declared. In addition, the Partnership (or a third-party with its prior written consent) may redeem the Series A Preferred Units following certain changes in the methodology employed by ratings agencies, changes of control or fundamental transactions as set forth in the Amended Partnership Agreement. If, upon a change of control or certain fundamental transactions, the Partnership (or a third-party with its prior written consent) does not exercise this option, then the holders of the Series A Preferred Units have the option to convert the Series A Preferred Units into a number of common units per Series A Preferred Unit as set forth in the Amended Partnership Agreement. The Series A Preferred Units are also required to be redeemed in certain circumstances if they are not eligible for trading on the New York Stock Exchange.

Holders of Series A Preferred Units will have no voting rights except for limited voting rights with respect to potential amendments to the Partnership Agreement that have a material adverse effect on the rights, preferences, obligations or privileges of the Series A Preferred Units, the issuance by the Partnership of certain securities, approval of certain fundamental transactions and as required by law.

Upon the transfer of any Series A Preferred Unit to a non-affiliate of the Company, the Series A Preferred Units will automatically convert into a new series of preferred units (the “Series B Preferred Units”) on the later of the date of transfer and the second anniversary of the date of issue. The Series B Preferred Units will have the same terms as the Series A Preferred Units except that unpaid distributions on the Series B Preferred Units will accrue on a cumulative basis until paid.

The foregoing description of the Purchase Agreement does not purport to be complete and is qualified in its entirety by reference to the text of the Purchase Agreement, which is filed as Exhibit 10.1 to this Current Report and is incorporated herein by reference.

Through its wholly-owned subsidiary, the Company owns approximately 55.4% of the limited partner interests in the Partnership (consisting of 94,151,707 common units and 139,704,916 subordinated units) (not including any of the Series A Preferred Units to be purchased in the Private Placement), 50% of the management rights in the General Partner, and a 40% interest in the incentive distribution rights in the Partnership held by the General Partner.

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.

INDEX TO EXHIBITS