The decision upheld a landmark decision by the Seoul High Court early last year that the National Health Insurance Service should provide equal spousal coverage to So Sung-wook and Kim Yong-min - a gay couple who filed a suit in 2021 against the agency which had cancelled their spousal benefits.
"I couldn’t believe when I heard the ruling. I was extremely happy and I started crying," Kim Yong-min told Reuters outside the court.
"It took four years to earn this dependent status and…we need to fight harder to legalize same sex marriage going forward," he said.
Chief Justice Jo Hee-de said that denying them such benefits because of gender, even though there are no clauses in the national health insurance act specifying it, constituted discrimination based on sexual orientation.
"It is an act of discrimination that violates human dignity and value, the right to pursue happiness, freedom of privacy and the right to equality before the law, and the degree of violation is serious," Jo told a televised trial.
So and Kim have held a wedding ceremony and are often described as a married couple but their marriage is not legally recognized in South Korea.
Lawyers and advocates said the ruling marks the first legal recognition of a same-sex union in South Korea.
A lower court had initially ruled in favour of the insurer because it argued a same-sex union could not be considered a common law marriage under the current law before the appellate court reversed the decision.
While campaigns to legalize same-sex marriage have succeeded in Taiwan and Thailand, there is no legal acknowledgment of LGBTQ partnerships in South Korea, forcing couples to move abroad if they want to get married legally.
The Supreme Court's ruling is a "stepping stone for progress" towards marriage equality, activist Horim Yi at Marriage For All, an LGBTQ campaign group, said.
"(Dependent status for health insurance) is one of the various rights that you can enjoy as a family, so it's going to be a very hopeful ruling for same-sex couples living in South Korea."
The couple hadsaid they were being visible and open about their story to help "change people's opinions and help other LGBTQ people like us gather up courage" in an interview with Reuters last year.
Conservative religious groups in South Korea have mounted fierce resistance to efforts to pass laws against discrimination, prompting many LGBTQ people to hide their identity in the workplace as they struggle for equal recognition and acceptance.
Ahead of the ruling, members of conservative Christian groups took part in a rally outside the court. They held up a banner reading "Same sex families are nonsense. Supreme Court, overturn the Seoul High Court's ruling!"
