A silent No vote is the only thing that can derail attempts to repeal the Eighth Amendment, it has been claimed as the Republic goes to the polls.
Yes campaigners were last night confident they have won over enough support to secure victory in today’s divisive vote.
But Taoiseach Leo Varadkar said they are “taking absolutely nothing for granted”.
More than 3.2 million people are entitled to make their voices heard on arguably the most contentious social issue in Ireland.
The Republic is being asked to make a “once in a generation” decision as senior political figures have categorically ruled out a rerun if the proposal to allow the Oireachtas to legislate for abortion is rejected.
The weather is not expected to impact on the turnout.
Met Eireann predicts a largely sunny day across the whole country, with just a few showers.
In the region of 120,000 people have added their name to the supplementary voting register in recent weeks and thousands of people have travelled home from abroad to cast their votes.
Health Minister Simon Harris said: “This is the moment so many people have waited so long for.
“It is an opportunity to face reality and to support women here in our own country.”
But Savethe8th’s John McGuirk said people must decide “whether or not we’re going to have a liberal abortion regime in Ireland”.
“The fear of a lot of people on the No side of the campaign is that every time you take the step we are being asked to take, you change the culture of the country.”
Mr McGuirk said the key to a No victory will be older voters.
“Whether they vote in large enough numbers to help us win the referendum is an open question,” he said.
At the same time he admitted some people who might be viewed as conservative on this issue will vote to repeal the Eighth as a “screw you” to the Catholic Church.
The question being asked of voters is whether they want to repeal a section of the constitution which gives equal rights to the mother and her unborn child.
A Yes vote result will clear the way for the Irish government to bring forward legislation that permits terminations up to 12 weeks into a pregnancy.
Mr Harris has promised that abortions will only be granted after the first trimester if there is a risk to the life, or of serious harm to the health of, a pregnant woman.
As campaigning drew to a close, Fianna Fail TD Mary Butler, who is part of the Love Both group reiterated her belief that the government has “cynically used the tragedies of certain people to push through the most extreme abortion law ever proposed in this country by any Irish”.
More than 2,000 people living off the coasts of Galway, Mayo and Donegal had their opportunity to vote yesterday.
The islands vote a day early in order to allow ballot boxes to make it back to the mainland for tomorrow’s count.
Gardai were last night escorting boxes to local court offices in each constituency.
They were due to be transferred to individual count centres in the early hours of this morning, before polls opened at 7am.
Mr Varadkar said if there is a Yes vote, Ireland “will still be the same country as it is today”.
“Of course we know when it comes to referendums in the past, like the divorce referendum, that went down to less than 10,000 votes, one ballot paper in every ballot box. We urge everyone to vote and vote yes,” he said.
“Opinion polls have been wrong before. I am conscious that in 1983 there was only a turnout of 55%, most people decided to sit out and I hope that won’t happen on this occasion and I am really encouraging everyone to come out and vote,” he said.
The Taoiseach said the fact that Irish women had to travel to another jurisdiction to end their pregnancies, and sometimes do so in secret, had created a legacy of shame.
“I hope that a Yes vote will help to lift that stigma and help to take away that legacy of shame that exists in our society,” Mr Varadkar said.
“If there is a Yes vote Ireland will be the same place, just a place that’s a little bit more compassionate and a little bit more understanding than it has been in the past.”
Thousands returned from around the world to make their voices heard, some from as far away as Asia and Latin America.
Ciaran Gaffney (22), from Argentina, said women should have complete bodily autonomy.
“I just think that we should not be exporting an issue like abortion to other countries and I think that we need to be responsible for taking charge of something that is happening in Ireland and will happen in Ireland irrespective of the vote.”
Aoife Bennett (25), an editor with a travel magazine based in Dortmund, Germany, will be making the journey back to Dublin then returning in less than 24 hours. She tweeted: “This is the most important referendum we may ever face. Of course I was coming home.”
Among those backing a No vote was Corrs musician Jim Corr.
The 53-year-old, who found fame with his sisters Andrea, Sharon and Caroline in Irish folk-rock band The Corrs, claimed the vote was a means for the pharmaceutical industry to profiteer from abortion.
He tweeted: “As many were duped into believing the Lisbon Treaty would bring jobs and recovery, many are being duped into believing this referendum is about healthcare and choice, when it’s really about bringing the lucrative abortion industry into Ireland.”