Sonia Sotomayor was sworn in Saturday as the Supreme Court's first Hispanic justice and only the third female member in the top United States court's 220-year history.

She is also President Barack Obama's first appointment to the court.

Sotomayor took the second of two oaths of office from Chief Justice John Roberts in an ornate conference room at the high court beneath a portrait of the legendary Chief Justice John Marshall. She swore a first oath in a private ceremony minutes earlier.

Sotomayor's mother, brother, other relatives and friends joined her for the occasion.

In one oath, she promised to support and defend the Constitution. In the second, she pledged to "administer justice" fairly and impartially.

Ideological balance

As a successor to liberal Justice David Souter, who retired, she is not expected to alter the nine-member court's ideological balance.

Sotomayor, 55, has been a federal judge for 17 years. Obama nominated her in May, and the Senate confirmed Sotomayor's nomination last Thursday.

Obama scheduled a White House reception for Sotomayor on Wednesday.

Sotomayor is the daughter of Puerto Rican parents who was raised in a housing project in New York City's gritty South Bronx neighbourhood and educated at the elite universities Princeton and Yale before going on to success in the legal profession and then the federal bench.

Sotomayor can now get to work, although the Supreme Court won't hear arguments until September 9 in a key campaign finance case. The entire court will convene a day earlier, however, for a formal ceremony to welcome Sotomayor.