Thailand's king has signed a marriage equality bill into law, making the country the first in South East Asia to recognise same-sex unions.

The bill cleared the Senate in June but required royal endorsement to become law. It was published in the Royal Gazette on Tuesday and will come into effect on 22 January next year.

Activists hailed the move as historic - it marks the culmination of years of campaigning for marriage equality. 

Thailand has long been seen as a relative haven for the LGBTQ+ community in a region where such attitudes are rare.

The new law uses gender-neutral terms in place of "husbands", "wives", "men" and "women". And it grants same-sex couples adoption and inheritance rights.

“Today we’re not only getting to write our names in marriage certificates, but we are also writing a page in history... that tells us that love never set a condition of who we were born to be," Ann Chumaporn, a longtime LGBTQ+ activist and co-founder of the Bangkok Pride movement, told the BBC.

"It’s a triumph of equality and human dignity."

She said she plans to organise a mass wedding for more than 1,000 LGBTQ+ couples on 22 January.

"[The legal recognition] means we are fully accepted and can live our lives without conditions or compromises," said advertising strategist Kwankaow Koosakulnirund.

"Thailand’s LGBTQ+ community can now look toward a future beyond relationships, embracing the sense of pride that this law brings," he said.

"We are all delighted and excited. We've been fighting for our rights for over 10 years, and now it's finally happening," another activist, Siritata Ninlapruek, told AFP news agency.

Prime Minister Paetongtarn Shinawatra posted on X: "Congratulations on everyone's love. #LoveWins."

Former PM Srettha Thavisin, who has been vocal in his support for the bill, also applauded the development as a "significant step" for Thailand.

"Equity and equality have become concrete in the Thai society. Gender diversity will eventually be fully accepted. Congratulations," he wrote on X.

When the law comes into effect, Thailand will become only the third place in Asia, after Taiwan and Nepal, where same-sex couples can get married.

In 2019, Taiwan's parliament became the first in Asia to legalise same-sex marriage. Nepal registered its first same-sex union in November last year, five months after its Supreme Court ruled in favour of it.

This was just one month after India's top court had ruled against it, leaving the decision to the government, which said it would set up a panel to decide on more legal rights for same-sex couples.

Singapore scrapped a colonial-era law that banned gay sex in 2022, but also amended its constitution to prevent the courts from challenging the definition of marriage as one between a man and a woman.