Shaping the court
Kagan, the former dean of Harvard Law School, will join two other women on the nine-member court, including Sonia Sotomayor, the first Hispanic supreme court justice, who was nominated by Obama and confirmed by the senate last year.
"When Elena takes her seat on that bench, for the first time in our history there will be three women"
"When Elena takes her seat on that bench, for the first time in our history there will be three women," Obama said in a statement.
"Today's vote wasn't just an affirmation of Elena's intellect and accomplishment, it was also an affirmation of her character and her temperament, her open-mindedness and even-handedness".
Kagan replaces former Justice John Paul Stevens, who retired in June after turning 90 in April.
Her appointment means the nine-member courtnow features four justices appointed by Democratic presidents and five by Republicans, although history has shown that justices often do not vote according to the politics of the president who chose them.
Kagan is also the first nominee in four decades to reach the supreme court without ever having served as a judge.
The debate over Kagan's nomination in the senate was coloured by the approaching November elections, which will decide one-third of seats in the senate and all of the House of Representatives.
Republicans painted Kagan as an enemy of gun rights and of curbs on abortion, and denounced her for setting limits on military recruitment at Harvard because of her disapproval of the "Don't Ask, Don't Tell" ban on gays serving openly.
Kagan's service in the administration of Bill Clinton, the former US president, also created concern amongst Republicans.
"Americans expect politics to end at the courtroom door," Mitch McConnell, the Republican leader in the senate, said.
"Nothing in Elena Kagan's record suggests that her politics will stop there."
There has been some speculation that Justice Ruth Bader Ginsburg, a 77-year-old cancer survivor whose husband died in June, would retire soon, giving Obama the chance to make the third supreme court appointment of his presidency.
But Ginsburg told the Associated Press this weekthat she hopes to stay on for at least another five years.