The margin of victory is tipped to be heading towards a 2:1 majority.
The Republic of Ireland appears set to become the first country to introduce same-sex marriage by a popular vote, especially now since the ‘no’ campaign appears to have conceded.
David Quinn, of the Iona Institute and ‘No’ campaign tweeted a concession and congratulations to the ‘Yes’ campaign amid widespread reports of a landslide.
In a statement the Iona institute said: “We would like to congratulate the Yes side on winning such a handsome victory in the marriage referendum.
“They fought a very professional campaign that in truth began long before the official campaign started.
“For our part, The Iona Institute is proud to have helped represent the many hundreds of thousands of Irish people who would otherwise have had no voice in this referendum because all of the political parties backed a Yes vote.
“The Iona Institute would like to thank the thousands of volunteers up and down the country who worked day and night to try and secure a No vote.”
David Quinn said: “Going forward, we will continue to affirm the importance of the biological ties and of motherhood and fatherhood. We hope the Government will address the concerns voters on the No side have about the implications for freedom of religion and freedom of conscience.”
CONGRATULATIONS to the Republic on saying yes to same-gender marriage! Now what about Northern Ireland?
The high turnout favoured Yes campaigners as the efforts to get the vote out worked effectively, particularly among young voters.
Few, if any locations, are showing a No vote winning the referendum.
Even in traditionally conservative rural area, the vote is coming in at 50:50.
Dublin will be strongly Yes, right across the city and county.
But this trend is being matched in locations across the country.
Sinn Fein President Gerry Adams said it was a good day for equality and a good day for Ireland.
He said: "It appears to be an overwhelming 'Yes' vote across the State. This is a very good day for equality and a very good day for Ireland.
"Irish people have demonstrated that we are a decent, tolerant and compassionate people.
"I want to commend all those who took part in the campaign over recent weeks and all those who voted, especially those who voted 'Yes'.
"I want to congratulate the Sinn Féin members across the State who worked hard for a 'Yes' vote and to thank the Sinn Féin 'Yes' Campaign Director, Pádraig Mac Lochlainn TD.
"During the campaign we heard a lot of talk from all political parties about the need for equality. We now need to see that sentiment extended to the social and economic sphere.
"Sinn Féin will continue to demand that all Government policies and budgets are equality proofed. This is essential if we are to construct a truly equal society.
“The marriage equality rights that will now be enjoyed by citizens in the south must be available to all in the north. Sinn Féin will continue to campaign for equal rights for all.
"Another very notable aspect of the campaign was the huge desire among our diaspora for the right to vote. It underlines the case that our emigrants should no longer be denied a voice in our democracy."
The very early tallies in Mayo, Wexford, Wicklow, Roscommon and Clare all signal a Yes vote.
The barometer constituency of Tipperary North is showing a 60:40 split.
A Fine Gael strategist said he expects the result to be up to 2:1 Yes vote.
"It'll be about 65-66pc carried across the board," the strategist said.
Labour Party junior minister Kevin Humphreys, who has a reputation for calling vote results early, says the vote will be Yes.
His estimates from his own constituency of Dublin South-East show some boxes coming across with results of anything up to 80pc Yes.
Although the areas concerned would be strongly liberal, the pattern indicates a strong Yes elsewhere.
"The trend is so big here, it has to be matched to a degree across the country," he said.
Fianna Fail leader Micheal Martin also said he believes it will be a strong Yes vote.
Mr Martin said he had never seen so many young people voting before.
The party leader also defended Fianna Fail's record in campaigning for a Yes vote.
Fianna Fail TD John McGuinness said he was voting No, while other TDs and Senators refused to say what way they were doing.
Mr Martin said a lot of his party did "put their shoulder to the wheels".
"It is not about parliamentary parties. That's the clear message from this campaign," he said.
"This is very much above and beyond and transcends party politics," he added.