Ireland's new laws on gay marriage will be enacted by the end of July, with the first ceremonies likely in the autumn.
The country becomes the first in the world to bring the change in by popular vote, with 62 per cent of the electorate backing it.
U2 frontman Bono has celebrated Ireland's vote for gay marriage.
On the second night of their latest tour in the US, the star dedicated Pride (In The Name Of Love), one of the band's top hits, to mark the historic day.
On stage, in front of thousands, he said: "It's a moment for us to thank the people who bring us peace to our country. We have peace in Ireland today ...and in fact on this very day we have true equality in Ireland,"
Ireland's new laws on gay marriage will be enacted by the end of July, with the first ceremonies likely in the autumn.
Ireland's overwhelming support for gay marriage is a message to the world, UN secretary general Ban Ki-moon said.
Billie asked girlfriend Kate to marry her at a count centre in Limerick moments after the result was announced.