UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)*

MARLIN BUSINESS SERVICES CORP.

(Name of Issuer)

Common Stock, $0.01 par value per share

(Title of Class of Securities)

571157106

(CUSIP Number)

Red Mountain Capital Partners LLC

Attn: Willem Mesdag

10100 Santa Monica Boulevard, Suite 925

Los Angeles, California 90067

Telephone (310) 432-0200

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

December 22, 2014

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box.  ¨

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 4 amends and supplements the Schedule 13D filed with the Securities and Exchange Commission (the “SEC”) on June 15, 2009, as amended by Amendment No. 1 thereto, filed with the SEC on December 21, 2009, Amendment No. 2 thereto, filed with the SEC on January 5, 2010, and Amendment No. 3 thereto filed with the SEC on May 18, 2011 (collectively, this “Schedule 13D”), by (i) Red Mountain Capital Partners LLC, a Delaware limited liability company (“RMCP LLC”), (ii) Red Mountain Capital Partners II, L.P., a Delaware limited partnership (“RMCP II”), (iii) Red Mountain Capital Partners III, L.P., a Delaware limited partnership (“RMCP III”), (iv) RMCP GP LLC, a Delaware limited liability company (“RMCP GP”), (v) Red Mountain Capital Management, Inc., a Delaware corporation (“RMCM”), and (vi) Willem Mesdag, a natural person and U.S. citizen, with respect to the common stock, $0.01 par value per share (the “Common Stock”), of Marlin Business Services Corp., a Pennsylvania corporation (“Marlin”). The filing of any amendment to this Schedule 13D shall not be construed to be an admission by the Reporting Persons that a material change has occurred in the facts set forth in this Schedule 13D or that such amendment is required under Rule 13d-2 of the Securities Exchange Act of 1934, as amended.

Item 2 of this Schedule 13D is hereby amended and restated as follows:

RMP was formed, and its principal business is, to invest in small cap public companies and to enhance shareholder value through active ownership. RMCP GP is the general partner of RMP and thus may be deemed to control RMP. RMI Series A was formed, and its principal business is, to invest in the Common Stock. RMCP Manager is the managing member of RMI Series A and thus may be deemed to control RMI Series A. RMCP LLC is the managing member of RMCP GP and the sole member of RMCP Manager and thus may be deemed to control RMCP GP and RMCP Manager and each entity directly or indirectly controlled by RMCP GP or RMCP Manager. RMCM is the managing member of RMCP LLC and thus may be deemed to control RMCP LLC and each entity directly or indirectly controlled by RMCP LLC. Mr. Mesdag is the president, sole executive officer, sole director and sole shareholder of RMCM and thus may be deemed to control RMCM and each entity directly or indirectly controlled by RMCM (including Red Mountain). The principal business of each of RMCP GP, RMCP Manager, RMCP LLC and RMCM is investment. The principal occupation of Mr. Mesdag is serving as an executive officer and Managing Partner of RMCP LLC. He is a U.S. citizen.

Each of J. Christopher Teets, Jack Watkinson and John Hill (and each of their principal occupations) is serving as an executive officer and Partner of RMCP LLC. None of Mr. Teets, Mr. Watkinson or Mr. Hill controls any Reporting Person. Information regarding Mr. Teets, Mr. Watkinson and Mr. Hill is being included in this Schedule 13D solely for purposes of complying with General Instruction C to Schedule 13D. Each of Mr. Teets, Mr. Watkinson and Mr. Hill is a U.S. citizen.

Item 3 of this Schedule 13D is hereby amended to include the following information:

Previously, 1,184,385 shares of Common Stock were reported as being held by RMCP II, and 75,517 shares of Common Stock were reported as being held by RMCP III. At the time, RMP owned 100% of the economic interests of RMCP II and RMCP III, and RMCP GP served as the general partner of each of RMP, RMCP II and RMCP III. As part of an internal restructuring, RMCP II and RMCP III distributed all Common Stock held by them to RMP in a transaction that resulted in a change in the form of beneficial ownership of such Common Stock but not a change in pecuniary interest in such Common Stock. As a result of such internal restructuring, RMP now directly holds such shares of Common Stock, and each of RMCP II and RMCP III has ceased to beneficially own any Common Stock and has been dissolved.

RMP and RMI Series A purchased a block of 1,705,317 shares of Common Stock at an aggregate purchase price (excluding trading commissions and related administrative costs) of $34,106,340. The source of the funds used by RMP and RMI Series A to purchase such shares was working capital of RMP and RMI Series A, respectively.

The information set forth in Item 5(c) below is hereby incorporated by reference into this Item 3.

Item 4 of this Schedule 13D is hereby amended to include the following information:

The information set forth in Item 6 below is hereby incorporated by reference into this Item 4.

Item 5 of this Schedule 13D is hereby amended and restated as follows:

RMI Series A beneficially owns, in the aggregate, 852,658 shares of Common Stock, which represent approximately 6.7% of the outstanding Common Stock. RMI Series A has the sole power to vote or direct the vote, and the sole power to dispose or direct the disposition, of all such 852,658 shares of Common Stock. Because RMCP Manager may be deemed to control RMI Series A, RMCP Manager may be deemed to beneficially own, and to have the power to vote or direct the vote, or dispose or direct the disposition of, all of the Common Stock beneficially owned by RMI Series A.

Because each of RMCP GP, RMCP LLC, RMCM and Mr. Mesdag may be deemed to control, directly or indirectly, RMP, each of RMCP GP, RMCP LLC, RMCM and Mr. Mesdag may be deemed to beneficially own, and to have the power to vote or direct the vote, or dispose or direct the disposition of, all of the Common Stock beneficially owned by RMP.

Because each of RMCP Manager, RMCP LLC, RMCM and Mr. Mesdag may be deemed to control, directly or indirectly, RMI Series A, each of RMCP Manager, RMCP LLC, RMCM and Mr. Mesdag may be deemed to beneficially own, and to have the power to vote or direct the vote, or dispose or direct the disposition of, all of the Common Stock beneficially owned by RMP.

The filing of this Schedule 13D shall not be construed as an admission that any Reporting Person is the beneficial owner of any of the shares of Common Stock that such Reporting Person may be deemed to beneficially own. Without limiting the foregoing sentence, each of RMCM and Mr. Mesdag disclaims beneficial ownership of all shares of Common Stock reported in this Schedule 13D. In addition, the filing of this Schedule 13D shall not be construed as an admission that any partner, member, director, officer or affiliate of any Reporting Person is the beneficial owner of any of the shares of Common Stock that such partner, member, director, officer or affiliate may be deemed to beneficially own. Without limiting the foregoing sentence, each of Mr. Teets, Mr. Watkinson and Mr. Hill disclaims beneficial ownership of all shares of Common Stock reported in this Schedule 13D.

Item 6 of this Schedule 13D is hereby amended and restated as follows:

To facilitate the transaction described in this Schedule 13D, RMP, RMCP GP LLC, RMCP and RMCM made certain customary passivity commitments to the Federal Reserve Board in a commitment letter (the “Commitment Letter”) to ensure that RMP, RMCP GP LLC, RMCP and RMCM and their affiliates will not, without the prior approval of the Federal Reserve Board or its staff, (i) exercise or attempt to exercise a controlling influence over the management or policies of the Company or any of its subsidiaries, (ii) own, control or hold with power to vote securities that represent 25% or more of any class of voting securities of Marlin or any of its subsidiaries, (iii) propose a director or slate of directors in opposition to a nominee or slate of nominees proposed by Marlin’s management or board of directors, (iv) solicit or participate in soliciting proxies with respect to any matter presented to Marlin’s shareholders or (v) dispose or threaten to dispose (explicitly or implicitly) of equity interests of Marlin in any manner as a condition or inducement of specific action or non-action by Marlin, among other things.

The foregoing reference to and description of the Commitment Letter do not purport to be complete and are subject to, and are qualified in their entirety by reference to, the full text of the Commitment Letter, which is filed as Exhibit 99.3 to this Schedule 13D and incorporated herein by reference.

Other than as described in this Schedule 13D, there are no contracts, arrangements, understandings or relationships among the persons named in Item 2 above and between such persons and any person with respect to any securities of Marlin.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: December 22, 2014

Exhibit 99.2

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) promulgated under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a Schedule 13D (including any amendments thereto) with respect to the common stock, $0.01 par value per share, of Marlin Business Services Corp. and further agree that this Joint Filing Agreement shall be included as an exhibit thereto.

The undersigned further agree that each party hereto is responsible for the timely filing of such Schedule 13D and any amendments thereto and for the completeness and accuracy of the information concerning such party contained therein; provided that no party is responsible for the completeness or accuracy of the information concerning any other filing party, unless such party knows or has reason to believe that such information is inaccurate. This Joint Filing Agreement may be executed in one or more counterparts, all of which shall constitute one and the same instrument.

IN WITNESS WHEREOF, each of the undersigned hereby executes this Joint Filing Agreement as of December 22, 2014.

Exhibit 99.3

EXECUTION COPY

Red Mountain

October 16, 2014

Red Mountain Partners, L.P., a Delaware limited partnership; RMCP GP LLC, a Delaware limited liability company; Red Mountain Capital Partners LLC, a Delaware limited liability company; Red Mountain Capital Management, Inc., a Delaware corporation (each, a “Red Mountain Acquirer”), and their subsidiaries and affiliates (collectively, “Red Mountain Acquirer Group”), will not, without the prior approval of the Board or its staff, directly or indirectly:

EXECUTION COPY

EXECUTION COPY

The terms used in these commitments have the same meanings as set forth in the Bank Holding Company Act of 1956, as amended, and the Board’s Regulation Y.

Nothing in these commitments releases the Red Mountain Acquirer Group from compliance with the Change in Bank Control Act of 1978, as amended, and any regulations thereunder for any subsequent acquisition or increase in the percentage ownership of any class of voting shares of Marlin.

Red Mountain Acquirer Group understands that these commitments constitute conditions imposed in writing in connection with the Board’s findings and decisions related to Red Mountain Acquirer Group’s acquisition of up to 24.9 percent of voting shares of Marlin, and, as such, may be enforced in proceedings under applicable law.