British national known as QT won a landmark court victory against the immigration department for their refusal to issue a spousal visa despite the fact the couple had a legal civil partnership in the UK.
The ruling that could pave the way for other gay partners to join their loved ones in the city.
In a unanimous decision reached by three judges, the Court of Appeal found that the director of immigration failed to justify the "indirect discrimination on account of sexual orientation that QT suffers."
The pair moved to the city in 2011.
In the 68-page ruling, judge Andrew Cheung wrote that "times have changed and an increasing number of people are no longer prepared to accept the status quo without critical thought".
"Excluding a foreign worker's lawfully married (albeit same-sex) spouse or civil partner ... to join the worker is, quite obviously, counter-productive to attracting the worker to come to or remain in Hong Kong to work in the first place," he added.
The city's first openly gay lawmaker, Ray Chan, called it a "big win for same-sex dependants to apply for a visa to stay in Hong Kong," according to Reuters.
The court ruled that QT and Hong Kong's Department for Immigration have 28 days to work out an arrangement.