But the White House and President Barack Obama's re-election campaign, eager to avoid a debate on a hot-button social issue in an election year, insisted that Biden was not breaking ranks with Obama, who does not publicly support gay marriage.
Biden told NBC's "Meet the Press" that marriage should be about being loyal to someone you love, whether that marriage is between a man and a woman, two men or two women. "I am absolutely comfortable with the fact that men marrying men, women marrying women and heterosexual men and women marrying one another are entitled to the same exact rights, all the civil rights, all the civil liberties," Biden said in the interview broadcast Sunday.
Gay rights advocates said Biden's comments signaled unmistakable support for gay marriage, which they said made him the highest-ranking member in the Obama administration to take that position.
"''I'm grateful that the vice president of the United States is now publically supporting marriage equality and I hope very soon the president and the rest of our leaders, Republicans and Democrats in Congress, will fall in line with the vice president," said Chad Griffin, a gay rights supporter and a member of the Obama campaign's national finance committee.
Joe Solmonese, the president of the Human Rights Campaign, said his group was encouraged by Biden's comments and called on Obama to speak out for "full marriage equality" for same-sex couples.
While Obama opposes gay marriage, he says his personal views on the matter are "evolving" and has noted that polls show Americans are increasingly supporting same-sex marriage.
Biden, a devout Catholic, has said previously that his personal views, as well as the country's, on gay marriage are evolving.
The vice president's office said Sunday after the interview aired that Biden's comments were not an endorsement of gay marriage, but simply a reaffirmation of his belief that same-sex couples deserve the same rights and protections as all Americans.
David Axelrod, a senior adviser to the Obama campaign, chimed in on Twitter, saying Biden and Obama share the view that all married couples should have the same legal rights.
For the Obama campaign, gay marriage has become a vexing election-year issue.
Each time the campaign promotes the president's extensive work in advancing gay rights, including ending the military's ban on openly gay service members, it is reminded of the one area where the president has fallen short in the eyes of gay rights advocates.
Several Democrats are pushing for Obama to include support for gay marriage in the party's platform, which will be finalized at the Democratic convention this summer.
Campaign officials have played down the notion that Obama's position on gay marriage will "evolve" before the November election. They say Obama's record in supporting other gay rights issues stands in stark contrast to his Republican challenger Mitt Romney, an ardent opponent of gay marriage and other benefits for same-sex couples.
One gay rights advocate said that even before the NBC interview, Biden had been hinting that his personal views of gay marriage may have evolved more quickly than the president's.
The advocate described a private meeting Biden had with about 30 gay and lesbian supporters in Los Angeles earlier this spring. When the vice president was asked about his personal views of gay marriage, the advocate said Biden told supporters that when his views differ from the president's, he often has to keep his opinions to himself.
This person spoke on condition of anonymity because participants at the meeting agreed not to discuss publicly what was said at the private gathering.
Biden did mention the Los Angeles event in his interview Sunday. He said that after meeting the children of the gay couple hosting the event, he told them he wished "every American could see the look of love those kids has in their eyes for you guys. And they wouldn't have any doubt about what this is about."