Sir Elton John has urged Northern Ireland politicians to "enter the 21st Century" over same-sex marriage and that if there was a public vote it would "sail in".
This week the Assembly voted in favour of the introduction of same-sex marriage for the first time.
However, a DUP petition of concern blocked the motion.
Northern Ireland remains the only part of the British Isles not to have legislated for same-sex marriage.
Elton John was asked about the matter on the BBC's Today programme on Radio 4.
He said: "God, if it can be voted for in southern Ireland by two to one.
"[In Northern Ireland] it's not a public vote, it's by the politicians and the politicians need to get their act together and enter the 21st Century.
"And I'm sure if there was a vote in Northern Ireland it would sail in."
The singer was in London to promote a new HIV/Aids partnership with the US government with his husband, David Furnish.
Asked if he would perform in Northern Ireland the musician responded: "Of yeah, why not?
"I'm not a politician, I bring hope through music.
"I will speak out for rights as when I can and especially LBGT rights as I'm an elderly gay citizen."
On Monday 53 MLAs voted for the first joint Sinn Fein/SDLP motion on the issue, asking the Executive to initiate legislation - with 52 against, a majority of just 50.5%.
But the motion was blocked by the DUP using the petition of concern mechanism, which means a motion must secure a majority of both unionists and nationalists.
It was the fifth time the issue had been debated at Stormont - Northern Ireland being the only part of the UK which has not passed same-sex marriage laws - but the first time it won a simple majority.