Trump's fellow Republicans voted to approve the judge, overcoming the unified opposition of Democrats.
Barrett, 48, is expected to take the oath of office at the White House on Monday night.
Her appointment seals for the foreseeable future a 6-3 conservative majority on the top US judicial body.
Only one Republican - Senator Susan Collins, who faces a tough re-election battle in Maine - voted against the president's nominee in Monday evening's vote.
Judge Barrett is the third justice appointed by the Republican president, after Neil Gorsuch in 2017 and Brett Kavanaugh in 2018.
The federal appeals court judge from Indiana fills the vacancy left by Justice Ruth Bader Ginsburg, a liberal icon who died last month.
Democrats had argued for weeks that it should be up to the winner of the 3 November election to pick the nominee.
The vote tilts the court further to the right in a victory for conservatives, reshaping the Court's ideological balance for years. Barrett fills the seat left vacant after the death of Ruth Bader Ginsburg.