The laws struck down included one enacted in 1977 and a statewide initiative approved by Californians in 2000, both limiting marriage to unions between a man and a woman. The ruling makes California the second state, after Massachusetts, to allow same-sex marriages.
The decision was denounced by pro-family groups, which promised to support an initiative proposed for the November ballot that would amend the California Constitution to ban same-sex marriages and overturn the decision.
Three of the four justices who issued the majority ruling were appointed by Republican governors.