WASHINGTON — The Senate confirmed Steven T. Mnuchin, a former Goldman Sachs banker and Hollywood film financier, to be Treasury secretary on Monday, putting in place a key lieutenant to President Trump who will help drive the administration’s plans to overhaul the tax code, renegotiate trade deals around the world and remake financial regulations.

By a vote of 53 to 47, the Senate confirmed Mr. Mnuchin, who was Mr. Trump’s top campaign fund-raiser. During a long debate over Mr. Mnuchin’s credentials, Democrats argued that his experience on Wall Street exemplified corporate malpractice that led to the 2008 financial crisis.

The new Treasury secretary will have little time to celebrate. He will be under pressure to help finalize the Trump administration’s tax plan, accelerate the rollback regulations and raise the government’s borrowing limit. The administration has said it will release a comprehensive plan to rewrite the tax code in the coming weeks, and it will have to deal with the debt ceiling next month.

While Mr. Mnuchin’s financial acumen has been praised by Mr. Trump and Republicans in Congress, Democrats have argued forcefully that he is not up to the job. They have painted him as a symbol of everything that is wrong with corporate America.