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.
Barack Obama’s appointment has to be ratified by the Senate, but its Republican majority has vowed to block a vote on any Supreme Court nominee from the current president.
Republicans have called on Barack Obama to leave the nomination to his successor, who will be elected in November.
The death of Justice Antonin Scalia, a staunch conservative, left the nine-member Supreme Court evenly divided between conservatives and liberals.
It also set off a battle in a presidential election year over Antonin Scalia’s successor.
Urging the Senate to support Merrick Garland, Barack Obama said: “He is the right man for the job. He deserves to be confirmed.”
President Barack Obama said Merrick 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, Barack Obama praised Merrick Garland’s decency, integrity and even-handedness during his long career in public service, and described him as an exemplary judge.
Merrick Garland was prepared to serve on the court immediately, he said.
Barack Obama expressed hope that Republicans would act in a bipartisan spirit and give Merrick Garland a “fair hearing”.
The nomination was the “greatest honor of my life”, Merrick Garland said.
Merrick 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.
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 Barack Obama of making the nomination “in order to politicize it for purposes of the election”.
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