With Thursday's law change, Thailand becomes the third - and by far the largest - country in Asia to allow same-sex marriages, after Taiwan and Nepal.
We are so happy, says 59-year-old Thanaphon Chokhongsung, who together with partner Sumalee Sudsaynet was the first to get married in the Bangkok district.
It's overwhelming. I can't even express my feelings in words, says 64-year-old Sumalee.
Many of the first couples were married at a gala in an exhibition hall in the capital.
We have fought for this for decades, says Sappanyoo Panatkool, who matched costumes with partner Apiwat Apiwatsayree.
With the new law, trans people can also get married in Thailand. All married couples will now also have the same rights regarding adoptions and inheritance.
"Today, the rainbow flag is waving proudly over Thailand", writes Prime Minister Paetongtarn Shinawatra in a post on X.
The bill was put to a vote in the country's senate in June last year. 130 of 152 present members voted yes.
Former Prime Minister Srettha Thavisin takes the opportunity to swing at the USA's new-old President Donald Trump, who on Monday issued a decree stating that there are "only two genders".
Recently, a country's leader said there are only two genders. I think we are more open-minded than that.
