A trans man, known as "K", filed the lawsuit nearly six years ago in light of what he described as "embarrassing and upsetting" discrimination often faced by trans people when using public bathrooms.

K was encouraged by doctors to use men's bathrooms as part of his gender dysphoria treatment, but because his Hong Kong ID card identified him as female, he could be fined up to HK$2,000 ($255) for doing so.

He did not receive criminal penalties but recalled a situation where his entering a women's bathroom led to tension and misunderstanding.

"The way people looked at me and doubted me was very painful," he told AFP.

"When the rules are abolished, I believe it will reduce these embarrassing situations."

K argued that existing rules breached his rights to equality, privacy, and freedom from discrimination.

High Court judge Russell Coleman agreed on Wednesday, saying the laws "create a disproportionate and unnecessary intrusion into the privacy and equality rights".

"Many trans people choose not to use public conveniences at all, due to fear, the threat of harassment, and to avoid having their gender identity invalidated or undermined," Coleman said.

The judge gave the government a year to "consider whether it wishes to implement a way to deal with the contravention".

Hong Kong's government said it would study the ruling and consider follow-up actions.

Transgender activists have notched a handful of wins in Hong Kong's courts, which are separate from those in mainland China.

The city's top court decided in 2023 that it was unconstitutional for the government to require a person to complete full gender-affirming surgery before the "sex entry" on their ID card could be changed.

K said the ruling was "another forward step" for LGBTQ rights but noted that Hong Kong still does not have a gender recognition law.

Authorities should also create more gender-neutral facilities and dispel myths that women's toilets would become unsafe after Wednesday's ruling, he added.

K's lawyer Mark Daly said the government has a duty to "proactively review discriminatory laws and ensure that public spaces are safe, inclusive, and accessible to all, regardless of gender identity".

Quarks, an advocacy group for transgender youth, hailed the ruling as a "major step for human rights development in Hong Kong".