The statement is more definitive than what White House spokesman Sean Spicer gave reporters last week. When he was asked on April 17 specifically if Trump will ever make his tax returns public, Spicer said, "We'll have to get back to you on that."
Trump has repeatedly claimed that he cannot release his returns because he is under audit by the IRS. The president previously said he would make those documents public when the audit is done.
When Spicer was asked last week if Trump would authorize the IRS to provide more details of the audit, the press secretary deflected. He said, "The president's view on this has been very clear" and "the American people understood it" when they elected him.
In a Wednesday briefing with reporters, Mnuchin said Trump has released "plenty of information."
But Trump's refusal to release his returns breaks decades of tradition. Almost all major presidential candidates since the 1970s have released their tax returns. Critics have argued that he should make more financial information public due to his wealth and potential ties to countries that could pose conflicts of interest while he's in office.
In demonstrations ahead of Tax Day earlier this month, protesters in several American cities urged Trump to release his tax returns. Trump criticized the demonstrations in tweets on April 16, claiming without citing evidence that someone "paid" the protesters and declaring "the election is over!"
— CNBC's Jacob Pramuk contributed to this report.