Marano, who joined ResCap in 2008, will remain as a member of the board.
Marano spent more than 25 years at now-defunct investment bank Bear Stearns & Co, where he was the global head of mortgage and asset-backed securities. Marano was managing director at Cerberus Capital Management before moving to ResCap.
ResCap filed for bankruptcy in May 2012 to protect its parent from mortgage liabilities that threatened to swamp the company. Ally is 74 percent-owned by the U.S. government after a series of bailouts.
Marano resignation comes at a time when creditors are awaiting a report from a court-appointed examiner, Arthur Gonzalez, about ResCap's relationship with Ally.
Warren Buffett's Berkshire Hathaway Inc (>> Berkshire Hathaway Inc.) <BRKb.N>, a ResCap creditor, asked the judge overseeing the ResCap bankruptcy for an investigation of what it called "potentially improper" pre-bankruptcy transactions between ResCap and Ally.
Gonzalez's report could provide leverage to creditors who want to hang a large portion of ResCap's liabilities of up to $25 billion on Ally.
Ally has offered $750 million to ResCap's estate in return for a release from liability.
Separately, ResCap late on Friday filed a complaint with the bankruptcy court seeking a declaration that its junior secured noteholders do not have a right to interest payments on their debt that accrued after ResCap filed for bankruptcy.
If ResCap succeeds, it could cut payments to holders of the junior secured notes by hundreds of millions of dollars, according to the court documents.
The ResCap bankruptcy case is In Re: Residential Capital LLC, U.S. Bankruptcy Court, Southern District of New York, No. 12-12020.
(Reporting by Tanya Agrawal in Bangalore and Tom Hals in Wilmington, Delaware; Editing by Supriya Kurane)