Senator David Norris, one of the key figures in having homosexuality decriminalised in the 1990s, has said the result of the Marriage Equality referendum is " wonderful".
Counting is under way in the landmark ballot which could see it become the first country in the world to bring in gay marriage by popular vote.
A high turnout is expected, which supporters of the reform believe is a boost for them, with estimates and reports from individual constituencies putting the poll percentage somewhere in the 60s.
A result is expected sometime in the afternoon but returning officers have warned it is dependent on how close the ballot is.
“I believe that by the end of today gay people will be equal in this country. I think it’s wonderful,” Senator Norris said.
“It’s a little bit late for me. As I said the other day I’ve spent so much time pushing the boat out that I forgot to jump on and now it’s out beyond the harbour on the high seas, but it’s very nice to look at.”
David Quinn, director of the Iona Institute and one of the most vocal campaigners, took to Twitter: “Congratulations to the Yes side. Well done.”
Congratulations to the Yes side. Well done. #MarRef— David Quinn (@DavQuinn) May 23, 2015
The Yes Equality group, which helped to spearhead the campaign for gay marriage, said Ireland would not return to the way it was for LGBT people regardless of whether the proposal is passed.
Co-director Grainne Healy said: “It has been extraordinary to see families voting together, friends voting as a group and new voters excited to be casting their very first vote on an issue which means so much to them.”
“We were going out not telling people to vote yes, we were going out saying I am voting yes and I’d like to tell you why. That’s how the campaign started and that’s how it has worked.”
Brian Sheehan, co-director of Yes Equality, said: “Witnessing young people return home to Ireland to their communities has been truly humbling.
“The marriage equality movement has ignited the imagination of a people to have an active part in the Ireland they want to live in and be proud of.”
Other countries have held referendums on gay marriage, including Croatia, Slovakia and Slovenia, where the extension of the right was not passed by the electorate.