President Barack Obama on Wednesday endorsed gay marriage.

Obama made his announcement during an interview with Good Morning America anchor Robin Roberts. Portions of the interview are to be broadcast Thursday on the ABC morning talk show.

Obama becomes the first sitting president in history to endorse marriage equality.

The president had previously said he backed civil unions and was “evolving” on marriage for gay couples.

The announcement comes just three days after Vice President Joe Biden said he was “comfortable” with gay couples marrying.

Marriage equality advocates cheered the news.

Chuck Wolfe, president and CEO of the Gay and Lesbian Victory Fund, a group which supports openly gay elected officials, called the announcement a “watershed moment for the LGBT civil rights movement.”

New York Assemblyman Daniel O'Donnell, who helped pass a gay marriage law in New York and recently married his partner of 31 years, said he was “thrilled.”

“As the President has previously acknowledged, for many, this is a changing, evolving issue,” O'Donnell said. “I'm very grateful that today, our President declared his support for equal treatment under the law for LGBT individuals across our country.”

“I commend President Obama for this brave and honest step,” said New York Congressman Jerrold Nadler, who has sponsored legislation to repeal the Defense of Marriage Act (DOMA). “Those who seek to politicize civil rights for personal or political gain will certainly attack him, but the course toward marriage equality and justice is the correct and inevitable path.”