Barrett is the first Supreme Court justice to be confirmed so close to a presidential election.
A conservative, Barrett fills the vacancy created by the September death of Justice Ruth Bader Ginsberg, who led the court’s liberal voting bloc.
Chief Justice John Roberts is set to administer a second oath — known as the judicial oath — to the former federal appeals court judge at a private ceremony at the court on Tuesday.
The 48-year-old Louisiana native will then be able to take part in the high court’s work. Her addition likely will solidify a 6-3 conservative shift on the nation’s highest court.