During an appearance at the Campus Progress National Conference in Washington on July 8, the former president said that he thinks it is "wrong for someone to stop someone else" from marrying.
"I personally support people doing what they want to do," Mr. Clinton said.
Mr. Clinton also said that he supports states' right to decide the legality of same-sex marriage and that he thinks "all these states that do it should do it." He said he does not believe it is a federal matter.
Mr. Clinton opposed same-sex marriage during his presidency. In 1996, he signed the Defense of Marriage Act, which defined marriage as a "legal union between one man and one woman" and prohibited the federal government from recognizing same-sex marriage.
During his tenure, Mr. Clinton also accepted a compromise establishing the "Don't Ask, Don't Tell" policy banning gay personnel from openly serving in the military.
Both of those policies have come under fire during the past few months as gay rights activists have become frustrated with the Obama administration. President Obama promised during the campaign to repeal both DOMA and "Don't Ask, Don't Tell," but his administration has taken little action on either front.
While Mr. Obama granted some rights to same-sex couples in the federal government, they did not include health care, and many complained the move was far from sufficient.
The state of Massachusetts filed a lawsuit against the federal government on July 8 saying DOMA interferes with the state's right to define marriage as it sees fit.
Mr. Clinton joins a slew of politicians whose opinions concerning gay marriage have changed over the years. The list includes Democratic National Committee chair Howard Dean, New York Senator Charles E. Schumer, New Jersey Governor Jon Corzine, and Connecticut Senator Christopher Dodd.
Unlike many conservative Republicans, former vice president Dick Cheney, who has a lesbian daughter, supports gay marriage, saying "people ought to be free to enter into any kind of union they wish, any kind of arrangement they wish."
A CBS News/New York Times poll last month found that 33 percent of Americans favor marriage for same-sex couples, down from a high of 42 percent in April, while another 30 percent support civil unions. A third of Americans think there should be no legal recognition of a same-sex couple's relationship.