Elena Kagan was sworn in Saturday afternoon as a U.S. Supreme Court justice.
Chief Justice John Roberts administered the oath at the Supreme Court building in Washington. Kagan beamed as a small invited audience cheered loudly.
The Supreme Court will meet in a special session on October 1 to hold an investiture ceremony for Kagan, Roberts said.
Kagan, the former solicitor general of the United States and former dean of the Harvard School of Law, is the fourth woman ever to serve on the nation's highest court.
The U.S. Senate confirmed Kagan on Thursday with a 63-37 vote.
She replaces retired Justice John Paul Stevens, leaving the court's liberal-conservative balance unchanged.