Elena Kagan was sworn in on Saturday as the 112th justice and fourth woman ever to serve on the Supreme Court.
Chief Justice John G. Roberts Jr. administered the oath to Ms. Kagan in a brief private ceremony at the court. Ms. Kagan, joined by family and friends, pledged to faithfully and impartially uphold the law.
Afterward, she smiled broadly as a crowd of onlookers stood and applauded. "We look forward to serving with you," Chief Justice Roberts said.
Justice Kagan, a former Harvard Law School dean who most recently was solicitor general, was President Obama's choice to succeed retired Justice John Paul Stevens. Republicans criticized her as a political liberal, before the Senate confirmed her this past week on a vote of 63-37.
She was sworn in twice Saturday by Chief Justice Roberts — reciting one oath as prescribed by the Constitution during a ceremony in a conference room at the court with only her family present. Justice Kagan then recited a second oath, taken by judges, with her family and friends and reporters present.
Justice Kagan won't be formally installed as a justice until Oct. 1 in a courtroom ceremony at the start of the court's new term. But after the oaths taken on Saturday, she will be able to begin assuming her duties as a justice, which include reviewing cases and emergency appeals filed to the Supreme Court.
Justice Kagan, 50, joins Justices Ruth Bader Ginsburg and Sonia Sotomayor on the nine-member court, which often divides 5-4 on high-profile cases such as gun rights, discrimination and campaign finance. The first woman in the court's history, Justice Sandra Day O'Connor, retired in 2005.
Justice Kagan isn't expected to alter the ideological balance of the court, where Justice Stevens was considered a leader of the liberals.