The legislation, backed by Conservative, Labor and Liberal Democrats leaderships, was approved by peers and parliament members earlier in the week.
With the assent of the queen, a ceremonial but required formality, the proposal became law. Same-sex marriages are expected to take place by summer of next year, the BBC said.
The law does not compel religious organizations to perform same-sex marriages but churches can "opt in" if they choose.
2014: The Year in Music [PHOTOS]