Obama said Sotomayor has more experience as a judge than any current member of the high court had when nominated, adding she has earned the "respect of colleagues on the bench, the admiration of many lawyers who argue cases in her court and the adoration of her clerks, who look to her as a mentor.''
Standing next to Obama at the White House, Sotomayor recalled a childhood spent in a housing project in the Bronx as well as her upper-echelon legal career: "I strive never to forget the real world consequences of my decisions on individuals, businesses and government.''
Barring the unexpected, Senate confirmation seems likely, given the large Democratic majority. If approved, she would join Justice Ruth Bader Ginsburg as the second woman on the current court, the third in history. She would succeed retiring Justice David Souter.
Senate Republicans pledged to give her a fair hearing, and some questioned whether she would base decisions on her personal feelings, rather than constitutional principles. Given her background, any effort to filibuster her nomination could carry political risks, since Hispanics are the fastest-growing segment of the population and an increasingly important one politically.
Sotomayor would be unlikely to alter the ideological balance of the court, since Souter generally sides with the liberals on key 5-4 rulings. But at 54, she is a generation younger that Souter, and liberal outside groups hope she will provide a counterpoint to some of the sharply worded conservative rulings.
Introducing his choice, Obama said, "Along the way, she's faced down barriers, overcome the odds and lived out the American dream that brought her parents here so long ago.''
The president called on the Senate to confirm Sotomayor before the court begins its new term in October, and noted pointedly that she has already won Senate approval twice in her career. Seven of the Senate's current Republicans voted to confirm her for the appeals court in 1998.
She was nominated a federal judge by a Republican, President George H.W. Bush, then elevated to the appeals court by a Democrat, Bill Clinton. Senate Republicans slow-walked her confirmation more than a decade ago, in part because she was viewed even then as a potential pick for the Supreme Court.
The White House announcement ceremony was a picture of diversity, the first black president, appointing the first Hispanic Supreme Court justice, joined by Vice President Joe Biden, who is white.
Sotomayor's nomination opens a new phase in the drive to replace Souter, as liberal and conservative groups alike scour the record she has compiled in 17 years on the federal bench.
In one of her most notable decisions, as an appellate judge she sided last year with the city of New Haven, Conn., in a discrimination case brought by white firefighters. The city threw out results of a promotion exam because too few minorities scored high enough. Coincidentally, that case is now before the Supreme Court.
That ruling has already drawn criticism from conservatives, and is likely to play a role in her confirmation hearing.
In one of her most memorable rulings as federal district judge, in 1995, Sotomayor ruled with Major League Baseball players over owners in a labor strike that had led to the cancellation of the World Series.
Obama referred to that in his remarks, then joked he hoped her support for the Yankees would not unduly influence New Englanders to oppose her in the Senate.
Among them is Sen. Patrick Leahy of Vermont, the chairman of the Senate Judiciary Committee, who said, "The American people will want the Senate to carry out its constitutional duty with conscientiousness and civility.''
The Senate Republican leader, Sen. Mitch McConnell of Kentucky, issued a statement that said: "Senate Republicans will treat Judge Sotomayor fairly. But we will thoroughly examine her record to ensure she understands that the role of a jurist in our democracy is to apply the law evenhandedly, despite their own feelings or personal or political preferences.''
In his remarks, Obama made no mention of his earlier statement that he wanted a justice with empathy, although his remark that compassion was needed came close.
Sotomayor grew up in New York after her parents moved from Puerto Rico. She has dealt with diabetes since age 8 and lost her father at age 9, growing up under the care of her mother in humble surroundings. As a girl, inspired by the Perry Mason television show, she knew she wanted to be a judge.
A graduate of Princeton University and Yale Law School, a former prosecutor and private attorney, Sotomayor became a federal judge for the Southern District of New York in 1992. She became an appeals judge in 1998 for the 2nd U.S. Circuit Court of Appeals, which covers New York, Vermont and Connecticut.
At her Senate confirmation hearing more than a decade ago, she said, "I don't believe we should bend the Constitution under any circumstance. It says what it says. We should do honor to it.''
Obama's nomination is the first by a Democratic president in 15 years.
One conservative group did not wait for the formal announcement. Wendy Long of the Judicial Confirmation Network, issued a statement calling Sotomayor a "liberal judicial activist of the first order who thinks her own personal political agenda is more important that the law as written.''
Abortion rights have been a flashpoint in several recent Supreme Court confirmations, although Sotomayor has not written any controversial rulings on the subject.
As a federal appeals court judge in 2002, she ruled against an abortion rights group that had challenged a government policy prohibiting foreign organizations receiving U.S. funds from performing or supporting abortions.
In her opinion, Sotomayor wrote that the government was free to favor the anti-abortion position over a pro-choice position when public funds were involved.
Sotomayor has spoken about her pride in her ethnic background and has said that personal experiences "affect the facts that judges choose to see.''
"I simply do not know exactly what the difference will be in my judging,'' she said in a speech in 2002. "But I accept there will be some based on my gender and my Latina heritage.''
From the moment Souter announced his resignation, it was widely assumed Obama would select a woman to replace him, and perhaps a Hispanic as well.
Obama came to office at a time when several potential vacancies loomed on the high court. Justice John Paul Stevens at is 89, and Ginsburg recently underwent surgery for pancreatic cancer.
