A lesbian expatriate, known to the court as QT, unanimously won her appeal against the Hong Kong Immigration Department, making her eligible to secure a dependent visa through her same-sex partner.
Such visas were previously restricted to only heterosexual couples.
The three appeals court judges said the department had failed to show that the visa scheme was put in place rationally.
Previously, a number of major multinationals and Out Leadership had filed a brief in the case asking for the court to find for QT.