Merrick Garland declared Obama's Supreme Court nominee
President Barack Obama has nominated veteran appeals court judge Merrick Garland to be the next US Supreme Court Justice.
The Supreme Court vacancy follows the death of Antonin Scalia last month.
Judge Garland, 63, is viewed as a moderate and has won praise from senior Republican figures.
The appointment has to be ratified by the Senate, but its Republican majority has vowed to block a vote on any Supreme Court nominee from Mr Obama.
Republicans have called on the president to leave the nomination to his successor, who will be elected in November.
The death of Justice Scalia, a staunch conservative, left the nine-member Supreme Court evenly divided between conservatives and liberals.
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The vacancy has become a major issue in the presidential election because the high court is often the final say on divisive issues such as abortion, immigration and climate change.
Urging the Senate to support Mr Garland, the US president said: "He is the right man for the job. He deserves to be confirmed".
President Obama said Mr Garland - chief judge of the Washington appeals court and a former prosecutor - enjoyed respect from Democrats and Republicans alike.
Announcing the nomination in the White House Rose Garden, Mr Obama praised Mr Garland's decency, integrity and even-handedness during his long career in public service, and described him as an exemplary judge.
Mr Garland was prepared to serve on the court immediately, he said.
President Obama expressed hope that Republicans would act in a bipartisan spirit and give Mr Garland a "fair hearing".
The nomination was the "greatest honour of my life", Mr Garland said.
Analysis: Anthony Zurcher, BBC News North America reporter
There were a lot of possible strategies being suggested as President Obama considered who would be his Supreme Court nominee. Would he opt for a young, outspoken liberal to rally his party's base and enact a generational ideological change on the court? Would he chose an underrepresented ethnicity or a woman that would force Republicans to risk angering some key voting bloc if they failed to confirm?
In the end Mr Obama chose accommodation by picking an older centrist in appellate court judge Merrick Garland.
It could be that Mr Obama still thinks there's a chance of Senate confirmation for a respected moderate. Maybe he thinks voters will be angered if the Senate rejects even the most uncontroversial choice.
Or perhaps Mr Garland was the best, most qualified candidate who would agree to go along with what will likely be a bruising, probably futile nomination process - a sacrificial lamb offered up in acknowledgment of a dire political reality.
One way or the other it's the Republicans' move now. They can accept Mr Garland or gamble that there won't be a new Democratic president next year who is itching for a fight.
Mr Garland was appointed by Democratic President Bill Clinton in 1997, winning confirmation in a 76-23 Senate vote, and served in the Justice Department during the Clinton administration prior to that.
Seven sitting Republican senators voted to confirm Mr Garland in 1997.
The White House also noted that when Mr Garland was previously considered for the Supreme Court, Republican Senator Orrin Hatch said the judge would be "very well supported by all sides".
Republicans again stressed they would defer action on a nomination to the Supreme Court until after the election.
Senate Republican majority leader Mitch McConnell said the American people should have a voice in filling the vacancy. He also accused Mr Obama of making the nomination "in order to politicise it for purposes of the election".
Supreme Court Nominee
Education: Harvard College and Law School
Current Job: Chief Judge, federal appeals court of Washington DC
Notable: Supervised investigations into the 1995 Oklahoma City bombing
Another Republican - Paul Ryan, the Speaker of the House of Representatives - said this had never been about who the nominee is.
"It is about a basic principle. Under our Constitution, the president has every right to make this nomination, and the Senate has every right not to confirm a nominee."
Senate Minority Leader Harry Reid said Republicans must act on the president's choice.
And a senior Democratic Senator, Chuck Schumer, described Merrick Garland as a "bipartisan choice".
He asked: "If the Republicans can't support him, who can they support?"