Mnuchin previously worked at Goldman Sachs for 17 years, where he rose to become partner. When he left Goldman, he founded RatPac Dune Entertainment, which financed several films, including "Avatar" and the X-Men movies.
The selection of Mnuchin as Trump's pick for treasury secretary, which requires Senate confirmation, marks the first major economic post filled by Trump. If confirmed to the position, this would be Mnuchin's first foray into the public sector.
During the campaign, Trump said he would dismantle the Obama administration's 2010 banking regulations known as Dodd-Frank, which Mnuchin has indicated should be re-examined.
"We're not taking a position on whether we support that or don't support it. We're saying a lot of things need to be looked at. We think Dodd-Frank needs to be looked at. Obviously there is an important concern of protecting depositors," Mnuchin said in a July interview with CNBC.
Democrats were quick to pounce on Trump's decision to pick Mnuchin to run the Treasury Department.
ABC News' Alana Abramson contributed to this report.
A previous version of this story described Steven Mnuchin as a billionaire. ABC News can’t independently verify his net worth.