U.S. Supreme Court Justice John Paul Stevens, seen in 2007, has announced his retirement. (Lucy Pemoni/Associated Press)

U.S. Supreme Court Justice John Paul Stevens, the court's oldest member and leader of its liberal faction, has announced he is retiring.

Friday's announcement came 11 days before his 90th birthday.

Stevens informed President Barack Obama in a letter he will step down when the court finishes its work for the summer in late June or early July. He said he hopes his successor will be confirmed "well in advance of the commencement of the court's next term."

Stevens has hinted at retiring in several interviews over the past several months.

President Barack Obama praised Stevens as an "impartial guardian" of the law and says he will move quickly to nominate a successor.

Stevens was a "brilliant" jurist who had "worn the judicial robe with honour and humility," Obama said.

Obama to choose successor

Obama now will have a chance to fill his second U.S. high court opening.

Obama's first Supreme Court nominee, Sonia Sotomayor, was confirmed by the U.S. Senate in August 2009 by a vote of 68-31.

The White House has plenty of time to settle on a successor. And Senate Democrats, who control 59 votes in the 100-member chamber, will conduct confirmation hearings and a vote. Republicans have not ruled out an attempt to delay confirmation.

The leading candidates to replace Stevens are Solicitor General Elena Kagan, 49, and federal appellate judges Merrick Garland, 57, and Diane Wood, 59.

Stevens's departure will not change the court's conservative-liberal split because Obama is certain to name a liberal-leaning replacement. But the new justice is not likely to be able to match Stevens's ability to guide narrow majorities in big cases.

Stevens was able to draw the support of the court's swing votes — now retired justice Sandra Day O'Connor and Justice Anthony Kennedy — to rein in or block some Bush administration policies, including the detention of suspected terrorists following the Sept. 11, 2001, attacks

Throughout his tenure, which began in 1975 after being nominated by President Gerald Ford, Stevens usually sided with the court's liberal bloc in the most contentious cases — those involving abortion, criminal law, civil rights and church-state relations.

In January, he dissented against a 5-4 Supreme Court ruling that eased decades-old limits on corporate spending in federal campaigns.

"The court's ruling threatens to undermine the integrity of elected institutions around the nation," Stevens said.

He also led dissenters in the landmark case that effectively decided the 2000 presidential election in favour of George W. Bush, following the Florida recount controversy.

With files from The Associated Press