President Michael D Higgins has signed Marriage Equality into law.
It means the Government can now bring forward legislation to allow same sex marriages to take place here.
This is expected to take place in September.
It follows the passing of the Marriage Referendum in May.
Ireland's human rights watchdog has welcomed the news this evening.
The Irish Council for Civil Liberties (ICCL) Executive Director Mr Mark Kelly said: "The President's decision today to sign into law the amendment of the Constitution opening full civil marriage to same sex couples is a vindication of the clearly-expressed wish of more than 1.2 million voters to live in a more equal Ireland.
"The ICCL warmly welcomes the fact that, following the recent dismissal by the Court of Appeal of spurious legal challenges to the landslide referendum result, marriage equality shall at last be the law of the land."