After graduating from college, Feinberg worked as a trader at Drexel Burnham in 1982 and later at Gruntal & Co.
In 1992, at the age of 32, Feinberg co-founded Cerberus Capital Management with William L. Richter and $10 million under management; by 2024; its assets under management would grow past $60 billion. In 1999, the firm hired former vice president Dan Quayle as a chairman of Cerberus Global Investment. In 2006, the firm hired former United States Secretary of the TreasuryJohn Snow, who serves as a chairman of Cerberus.
In May 2011, Feinberg stated that he believed residential mortgage-backed securities may present "a real opportunity for continued investment for quite a period of time" and that there were opportunities in buying assets from European banks.
Feinberg has said of the pay received by himself and other private equity executives, "In general, I think that all of us are way overpaid in this business. It is almost embarrassing." He has also noted in comments made in 2011 that smaller private equity fund sizes may be better for investor returns: "If your goal is to maximize your return as opposed to assets under management, I think you can be most effective with a big company infrastructure and a little bit smaller fund size."
Feinberg has been described as "secretive" in The New York Times. In 2007, Feinberg controversially told Cerberus shareholders, "If anyone at Cerberus has his picture in the paper and a picture of his apartment, we will do more than fire that person. We will kill him. The jail sentence will be worth it."
Cerberus owned DynCorp, a major private security contractor, from 2010 to 2020, leading to accusations of a conflict of interest during Feinberg's service on the President's Intelligence Advisory Board, and again after his nomination as Deputy Secretary of Defense.
Feinberg is a major Republican Party donor. In 2016, he served on the Trump Economic Advisory Council during Donald Trump's presidential campaign, donated nearly $1.5 million to pro-Trump PACs, and co-hosted a $50,000-per-person fundraising dinner for Trump and the Republican National Committee.
On March 14, 2025, Feinberg was confirmed by the United States Senate with a 59–40 vote. He was sworn in as the 36th United States Deputy Secretary of Defense on March 17, 2025. Feinberg filed paperwork saying he divested from Cerberus, but the paperwork included a clause showing he retains a financial relationship with the firm.
Under Feinberg's leadership, Pentagon officials have been directed to make unprecedented equity investments in private companies, including foreign entities. One key mechanism for doing so is funding through the Department's Office of Strategic Capital, led by Feinberg ally and former Cerberus executive David Lorch. The legality of these mechanisms has been under dispute within the Trump administration and among lawmakers.
Feinberg has also sought to receive proprietary information from contractors and companies as a condition of receiving federal funding, raising concerns about data privacy, cybersecurity, and government overreach. In September 2026, U.S. Secretary of CommerceHoward Lutnick was tapped to review Pentagon deals with Cerberus-linked companies in response to concerns about conflicts of interest from Feinberg and his deputies.
As of August 2026, Feinberg was also tapped to play a key role in restocking dwindling U.S. munition supply.
