WASHINGTON — The Senate confirmed Steven T. Mnuchin, a former Goldman Sachs banker and Hollywood film financier, to be secretary of the Treasury Department 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 and remake financial regulations.

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

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During his confirmation hearing before the Senate Finance Committee last month, Mr. Mnuchin was scolded by Democrats for failing to disclose nearly $100 million in assets and for not revealing his role as a director for an investment fund based in the Cayman Islands, a well-known tax haven. Republicans on the committee broke with protocol and pushed Mr. Mnuchin’s vote to the Senate floor after a boycott by Democrats.

Mr. Mnuchin, 54, is the latest member of Mr. Trump’s cabinet to edge through the confirmation process on a largely party-line vote. Last week, Tom Price was approved as secretary of health and human services and Betsy DeVos narrowly won confirmation to lead the Education Department.

The new Treasury secretary will have little time to celebrate. He will be under pressure to help finish the Trump administration’s tax plan, to accelerate the rollback of regulations and to raise the government’s borrowing limit.