Hillary Clinton endorsed marriage equality in a video message released Monday on the website of the gay-rights advocacy group, the Human Rights Campaign.
"Marriage, after all is a fundamental building block of our society; a great joy and, yes, a great responsibility," Clinton said in the video.
"To deny the opportunity to any of our daughters and sons solely on the basis of who they are and who they love is to deny them the chance to live up to their own God-given potential," she added.
Clinton, who stepped down as Secretary of State earlier this year, is considered to be a potentially field-clearing contender for the Democratic Party's presidential nomination in 2016. She now joins the likes of fellow Democrats President Barack Obama and Vice President Joe Biden, as well as Republican U.S. Senator Rob Portman in supporting marriage equality.
Clinton had supported civil unions for gay couples when she ran for president.
Earlier this month, her husband, former President Bill Clinton, urged the Supreme Court to overturn the Defense of Marriage Act, a law prohibiting federal recognition of same-sex couples that he signed into law in 1996.
In 2011, President Clinton the couple's daughter Chelsea teamed up to lobby New York lawmakers to back a law recognizing gay marriage. Hillary Clinton expressed support for the New York law after it passed but stopped short of changing her stance.
Her new position puts her in line with the majority of Americans. Some 53 percent of adults in the country endorsed same-sex marriage in a November Gallup poll. 
In her remarks, Clinton noted the dramatic shift that has taken place in public opinion, while also cautioning that more work needs to be done.
"For those of us who lived through the long years of the Civil Rights and women's rights movement, the speed with which more and more people have come to embrace the dignity and equality of LGBT Americans has been breathtaking and inspiring," Clinton said
"But the journey is far from over and therefore we must keep working to make our country freer and fairer," she concluded.