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 30, 2015

TARGA RESOURCES PARTNERS LP

(Exact name of registrant as specified in its charter)

1000 Louisiana, Suite 4300

Houston, TX 77002

(Address of principal executive office and Zip Code)

(713) 584-1000

(Registrants’ telephone number, including area code)

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:

Item 1.01 Entry into a Material Definitive Agreement.

Purchase Agreement

On January 15, 2015, Targa Resources Partners LP (the “Partnership”) entered into a Purchase Agreement (the “Purchase Agreement”), among the Partnership, its wholly-owned subsidiary, Targa Resources Partners Finance Corporation (“Finance Corp” and together with the Partnership, the “Issuers”), certain subsidiary guarantors named therein (the “Guarantors”) and Merrill Lynch, Pierce, Fenner & Smith Incorporated, Barclays Capital Inc., RBS Securities Inc., Morgan Stanley & Co. LLC and J.P. Morgan Securities LLC, as representatives of the several initial purchasers (the “Initial Purchasers”), pursuant to which the Issuers agreed to issue and sell to the Initial Purchasers $1,100,000,000 in aggregate principal amount of the Issuers’ 5% senior unsecured notes due 2018 (the “Notes”). The Notes were sold at par to yield 5% to maturity, resulting in gross proceeds to the Partnership of $1,091,750,000.

The Purchase Agreement contains customary representations and warranties of the parties and indemnification and contribution provisions under which the Issuers and the Guarantors, on the one hand, and the Initial Purchasers, on the other, have agreed to indemnify each other against certain liabilities, including liabilities under the Securities Act of 1933, as amended (the “Securities Act”).

Indenture

On January 30, 2015, in connection with the issuance of the Notes, the Partnership entered into an Indenture (the “Indenture”), among the Issuers, the Guarantors and U.S. Bank National Association, as trustee (the “Trustee”).

On January 30, 2015, the Notes were issued pursuant to the Indenture in a transaction exempt from the registration requirements under the Securities Act. The Notes were resold within the United States only to qualified institutional buyers in reliance on Rule 144A under the Securities Act, and outside the United States only to non-U.S. persons in reliance on Regulation S under the Securities Act.

The Notes will mature on January 15, 2018, and interest is payable on the Notes semi-annually in arrears on each January 15 and July 15, commencing July 15, 2015. The Notes are guaranteed on a senior unsecured basis by the Guarantors.

If the Partnership does not successfully complete its proposed merger with Atlas Pipeline Partners, L.P. (“APL”) on or prior to June 30, 2015, or if the related merger agreement is terminated prior to the completion of such merger, then the Issuers will redeem all of the Notes at a price equal to 100% of the initial offering price of the Notes, plus accrued and unpaid interest to the redemption date.

If by the 90th day (or such earlier day as the Partnership may elect) after the completion of the Partnership’s proposed merger with APL, the Partnership and/or the APL Issuers (as defined in the Indenture) have not repurchased or retired at least $500.0 million of the APL Notes (as defined in the Indenture) pursuant to the Partnership’s cash tender offers for the APL Notes or the change of control provisions of the indentures governing the APL Notes or otherwise, the Partnership will redeem $500.0 million aggregate principal amount of the Notes at a redemption price equal to 100% of the initial offering price of the Notes plus accrued and unpaid interest on the Notes redeemed, to the applicable redemption date.

At any time prior to October 15, 2017, the Issuers may redeem the Notes at a redemption price equal to the greater of (i) 100% of the principal amount of the Notes to be redeemed or (ii) the sum of the present values of the remaining scheduled payments of principal and interest on the Notes to be redeemed that would be due if the Notes matured on October 15, 2017, discounted to the redemption date on a semiannual basis at the Adjusted Treasury Rate (as defined in the Indenture) plus 50 basis points, together with accrued and unpaid interest to the date of redemption. On and after October 15, 2017, the Issuers may redeem some or all of the Notes at a redemption price equal to 100% of the principal amount of the Notes to be redeemed plus accrued and unpaid interest to the redemption date.

The Indenture restricts the Partnership’s ability and the ability of certain of its subsidiaries to, among other things: (i) incur additional debt or enter into sale and leaseback transactions; (ii) pay distributions on, or repurchase, equity interests; (iii) make certain investments; (iv) incur liens; (v) enter into transactions with affiliates; (vi) merge or consolidate with another company; and (vii) transfer and sell assets. These covenants are subject to a number of important exceptions and qualifications. If at any time the Notes are rated investment grade by either Moody’s Investors Service, Inc. or Standard & Poor’s Ratings Services and no Default or Event of Default (as each are defined in the Indenture) has occurred and is continuing, many of such covenants will terminate and the Partnership and its subsidiaries will cease to be subject to such covenants.

The Indenture provides that each of the following is an Event of Default: (i) default for 30 days in the payment when due of interest on, or liquidated damages, if any, with respect to, the Notes; (ii) default in the payment when due of the principal of, or premium, if any, on the Notes; (iii) failure by the Issuers or any Guarantor to make a change of control offer or an asset sale offer within the requisite time periods, to consummate a purchase of Notes when required under the Indenture or to comply with certain covenants relating to mandatory redemption of the Notes or merger, consolidation or sale of assets; (iv) failure by the Partnership to comply for 90 days after notice with the provisions of the Indenture relating to periodic reports of the Partnership as required by the Securities Exchange Act of 1934; (v) failure by the Issuers or any Guarantor to comply for 60 days after written notice with any of the other agreements in the Indenture; (vi) default under any mortgage, indenture or instrument under which there may be issued or by which there may be secured or evidenced any indebtedness for money borrowed by the Partnership or any of the Partnership’s restricted subsidiaries (or the payment of which is guaranteed by the Partnership or any of its restricted subsidiaries), if that default: (a) is caused by a failure to pay principal of, or interest or premium, if any, on such indebtedness prior to the expiration of the grace period provided in such indebtedness on the date of such default (a “Payment Default”); or (b) results in the acceleration of such indebtedness prior to its stated maturity, and, in each case, the principal amount of any such indebtedness, together with the principal amount of any other such indebtedness under which there has been a Payment Default or the maturity of which has been so accelerated, aggregates in excess of 3.0% of the Partnership’s consolidated net tangible assets, provided, however, that if, prior to any acceleration of the Notes, (a) any such Payment Default is cured or waived, (b) any such acceleration of such indebtedness is rescinded, or (c) such indebtedness is repaid during the 30 day period commencing upon the end of any applicable grace period for such Payment Default or the occurrence of such acceleration of such indebtedness, as applicable, any Default or Event of Default (but not any acceleration of the notes) caused by such Payment Default or acceleration of such indebtedness shall automatically be rescinded, so long as such rescission does not conflict with any judgment, decree or applicable law; (vii) failure by either Issuer or any of the Partnership’s restricted subsidiaries to pay final judgments aggregating in excess of 3.0% of the Partnership’s consolidated net tangible assets, which judgments are not paid, discharged or stayed for a period of 60 days; (viii) except as permitted by the Indenture, any subsidiary guarantee shall be held in any judicial proceeding to be unenforceable or invalid or shall cease for any reason to be in full force and effect or any Guarantor, or any person acting on behalf of any Guarantor, shall deny or disaffirm its obligations under its guarantee of the Notes; and (ix) certain events of bankruptcy or insolvency described in the Indenture with respect to the Issuers or any of the Partnership’s significant subsidiaries or any group of restricted subsidiaries that, taken as a whole, would constitute a significant subsidiary. In the case of an Event of Default arising from certain events of bankruptcy or insolvency with respect to either Issuer, all outstanding Notes will become due and payable immediately without further action or notice. If any other Event of Default occurs and is continuing, the Trustee or the holders of at least 25% in principal amount of the then outstanding Notes may declare all the notes to be due and payable immediately.

Registration Rights Agreement

On January 30, 2015, in connection with the issuance of the Notes, the Partnership entered into a Registration Rights Agreement among the Issuers, the Guarantors and the Initial Purchasers. Pursuant to the Registration Rights Agreement, unless the restrictive legend has been removed from the Notes and the Notes are freely tradable pursuant to Rule 144 under the Securities Act as of the 370th day following the issuance of the Notes, the Issuers and the Guarantors will (1) use commercially reasonable efforts to consummate an exchange offer and (2) if required, have a shelf registration statement declared effective with respect to resales of the Notes. The Issuers and the Guarantors are required to pay additional interest if they fail to comply with their obligations to exchange or register the Notes within the specified time periods.

Relationships

The Initial Purchasers or their respective affiliates have performed investment banking, financial advisory and commercial banking services for the Partnership and certain of its affiliates, for which they have received customary compensation, and they may continue to do so in the future. The Partnership has entered into swap transactions with certain of the Initial Purchasers and has agreed to pay these counterparties a fee in an amount the Partnership believes to be customary in connection with these transactions.

The descriptions set forth above in Item 1.01 are qualified in their entirety by the Purchase Agreement, the Indenture and the Registration Rights Agreement, which are filed herewith as Exhibits 10.1, 4.1 and 4.2 and are incorporated herein by reference.

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

The information included in Item 1.01 of this Current Report on Form 8-K is incorporated by reference into this Item 2.03 of this Current Report on Form 8-K.

Item 8.01 Other Events.

On January 15, 2015, the Partnership issued a press release announcing its commencement of its offering of the Notes. The Partnership is filing a copy of the press release as Exhibit 99.1 hereto, which is incorporated by reference to this Item 8.01.

Also on January 15, 2015, the Partnership issued a press release announcing the pricing of the Notes. A copy of the Partnership’s press release is filed as Exhibit 99.2 hereto and is incorporated by reference into this Item 8.01.

Each of the press releases shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state in which the offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state.

Item 9.01 Financial Statements and Exhibits.

(d) 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 thereunto duly authorized.

INDEX TO EXHIBITS