Thai advocates for LGBTQ rights hailed a major step forward Wednesday as the parliament passed a same-sex marriage bill in a landslide, paving the way for the nation to become the first in Southeast Asia to recognise marriage equality.

While Thailand enjoys a welcoming reputation for the international LGBTQ community, Thai activists have struggled for decades against conservative attitudes and values.

The bill sailed through on 399 to 10 votes in the lower house, although it must still be approved by the Senate and endorsed by the king before becoming the law of the land.

"Thailand is finally accepted and recognised as truly 'paradise for LGBTQI'," Chanya Rattanathada, 27, told AFP in the halls outside the voting chamber.

Inside, a small burst of cheers and clapping accompanied the final vote, with one representative waving a rainbow flag.

"Today, society has proved to us that they care about LGBT rights," said Tunyawaj Kamolwongwat, an MP with the progressive Move Forward Party, which has long pushed for LGBTQ rights.

"Now we finally will have the same rights as others."

The proposal will change references to "men", "women", "husbands" and "wives" in the country's marriage law to gender-neutral terms.

Prime Minister Srettha Thavisin said he was "proud of our pride" following approval of the bill.

"The passing (of this law) in the parliament today is a proud moment for Thai society who will walk together towards social equality and respect differences," he wrote on social media website X.

Across Asia only Taiwan and Nepal recognise same-sex marriage. Last year, India's highest court deferred the decision to parliament, and Hong Kong's top court stopped just short of granting full marriage rights.

  'Making everyone equal' 

 "It's a huge step for our country -- it is the first in Southeast Asia," Mookdapa Yangyuenpradorn, a spokesperson with activist group Fortify Rights, told AFP.

Mookdapa expressed hope that the later stages of the bill would progress smoothly, so that her country "will be on par with the international level in terms of LGBT rights".

The vote follows a decision by Srettha's cabinet last year that gave the go-ahead for the parliament debate.

The prime minister has been vocal in his support for the LGBTQ community, making the marriage equality policy a signature issue and telling reporters last year that the change would strengthen family structures.

Following the vote, Pheu Thai party spokesperson Danuphorn Punnakanta welcomed the decision of the lower house.

"Today, Thailand is one step ahead in terms of making everyone equal," he said.

Describing the law as one for "all Thai people", he emphasised that it would not violate heterosexual couples' rights -- but expand them for all relationships.

"It's only a win-win situation."

While Thailand has a reputation for tolerance, much of the Buddhist-majority country remains conservative and LGBTQ people, while highly visible, still face barriers and discrimination.

Activists have been pushing for same-sex marriage rights for more than a decade, but in a kingdom where politics is regularly upended by coups and mass street protests, the advocacy did not get far.

In 2022 Thai lawmakers gave initial approval to two bills that would allow same-sex marriages and two others that would permit civil partnerships.

But the legislation was dropped when parliament was dissolved to pave the way for a general election held last year.

Outside parliament, 18-year-old Plaifah Kyoka Shodladd told AFP there was a lot of excitement around the new law as it moved towards final approval.

But for now, they said: "We are happy."