President Joe Biden will on Tuesday sign into law a bill granting federal protections to same-sex marriage -- gathering thousands of guests at the White House to celebrate the legislative milestone.

It comes 12 years after Biden -- then Barack Obama's vice president -- took a public stand in favor of same-sex unions, well before they became legal in the entire United States through a 2015 US Supreme Court decision.

After the Supreme Court -- now significantly more conservative -- overturned longstanding abortion rights last June, lawmakers from the left and right came together to prevent any subsequent move to curb same-sex marriage rights, feared by some.

The legislation's final adoption by Congress last week marked a rare show of bipartisanship in deeply divided Washington.

In celebration, Biden will be gathering a group of Republican and Democratic lawmakers on the White House grounds, along with advocates and plaintiffs in marriage equality cases across the country, his spokeswoman Karine Jean-Pierre said Monday.

Jean-Pierre, who herself made history as the first openly gay White House press secretary, also touted "musical guests and performances to celebrate this historic bill."

The legislation, she said, "will give peace of mind to millions of LGBTQI+ and interracial couples who will finally be guaranteed the rights and protections to which they and their children are entitled."

Growing support

Hundreds of thousands of same-sex couples have married since the Supreme Court's 2015 decision legalizing the unions throughout the United States.

Public acceptance has grown dramatically in recent decades, with polls now showing a strong majority of Americans supporting same-sex marriage.

But some conservatives and the religious right remain opposed.

The new legislation, known as the Respect for Marriage Act, does not require states to legalize same-sex marriage but does require them to recognize a marriage so long as it was valid in the state where it was performed.

It repeals previous legislation defining marriage as a union between a man and a woman, and also protects interracial couples by requiring states to recognize legal marriages without regard to "sex, race, ethnicity or national origin."

In the House of Representatives, 39 Republicans joined a united Democratic majority in supporting the bill, while 169 Republicans voted against. It was previously adopted in the evenly-split Senate by 61 votes to 36.

'Who do you love?'

Jean-Pierre said Biden would stress Tuesday that "there is much more work to be done to protect LGBTQI+ individuals across the country."

Biden's spokeswoman recalled that the 80-year-old Democrat was among the first American political leaders to publicly support same-sex unions at the highest levels of government.

Back in 2012, Biden caused a stir by candidly declaring his support for same-sex unions -- when Obama's White House was still looking for the best way to make the president's position official as he sought reelection to a second term.

"I am absolutely comfortable with the fact that men marrying men, women marrying woman and heterosexual men marrying women are entitled to the same, exact rights," Biden said in a televised interview at the time.

"Who do you love? Who do you love and will you be loyal to the person you love?" Biden said. "That's what people are finding out what all marriages at their root are about."

Following his election in 2020, Biden tapped Pete Buttigieg to become his transport secretary -- the first openly gay person to be confirmed by the Senate to a cabinet post.

And beyond the issue of marriage, the Biden administration has taken a strong stance in support of LGBTQ rights -- notably towards the transgender community whose push for greater rights has become a political flashpoint in the country.

The administration has introduced gender-neutral passports -- allowing people who identify neither as male nor female to select the gender "X" -- and it lifted a ban on transgender people serving in the armed forces, introduced under Biden's predecessor Donald Trump.

© Agence France-Presse