The 48-year-old conservative jurist vowed to judge legal cases impartially.
But her selection so close to the 3 November presidential election has sparked a political battle between Republicans and Democrats.
The panel’s top Republican began by predicting a “contentious week” ahead.Judge Barrett’s approval would cement a 6-3 conservative majority on the nine-member court, shifting its ideological balance for potentially decades to come.
President Trump picked Judge Barrett to replace liberal Justice Ruth Bader Ginsburg, who died last month aged 87.
The Republicans – who currently hold a slim majority in the US Senate, the body that confirms Supreme Court judges – are trying to complete the process before Mr Trump takes on Democratic rival Joe Biden in the election.
The court’s nine justices serve lifetime appointments, and their rulings can shape public policy on everything from gun and voting rights to abortion and campaign finance.