The Senate confirmed former Representative Sean Duffy as secretary of transportation on Tuesday over a sudden swell of opposition from Democrats protesting the Trump administration’s sweeping freeze of federal grants, loans and other aid.

The final vote, 77 to 22, came after Mr. Duffy had appeared to be set to sail through with little to no opposition on Monday, when all Democrats had voted to advance his nomination.

Senator Chris Coons, Democrat of Delaware, said he initially backed Mr. Duffy because of his commitment to fund approved infrastructure projects. But Mr. Coons changed his mind after the White House’s order to pause a vast swath of federal aid set off confusion, outrage and threats of legal action around the country.

“In light of President Trump’s disastrous and illegal order last night to freeze all federal aid, including millions for those very transportation investments, I could not support Mr. Duffy’s nomination or any of President Trump’s nominees for the duration this directive is in place,” Mr. Coons said.

The showdown over the funding freeze cast a shadow over what had been one of Mr. Trump’s less contentious cabinet appointments.

During his confirmation hearing this month, Mr. Duffy had committed to improving roadway safety and tackling challenges within the aviation system. His testimony before the panel included discussions on critical topics like the oversight of the aerospace giant Boeing and the potential contributions of electric vehicle drivers to the Highway Trust Fund.