Abortion is now illegal in Ireland and has been since 1983 when an amendment was made requiring authorities to equally protect the right to life of a mother and that of a fetus, from the moment of conception.
Turnout could be higher than for the vote on same-sex marriage three years ago, said Irish national broadcaster RTE. Votes are expected to be counted on Saturday morning, with an official result to be declared later that day.
They say it's a once-in-a-generation opportunity to liberalise some of Europe's strictest abortion rules.
"More and more people are realising that this government has planned to introduce an extreme abortion law, the only way to stop this is to vote "No", said Mary Butler, an anti-abortion lawmaker from the main opposition party, Fianna Fail. The pollster says it interviewed some 4,000 people and the survey had a margin of error of plus or minus 1.5 percentage points.
The eighth amendment to the Irish constitution was installed following a 1983 referendum which approved outlawing abortion.More news: Sebastian, Vero Beach to get minimal impact from Tropical Storm Alberto
As the vote date approached, the debate between the two sides had grown deeply contentious, which, in part, motivated a lot of Irish ex-patriots to fly home from around the globe to cast their ballots - many posting their positions on social media beside the hashtag #HomeToVote. This grants unborn babies as much of an equal right to life as the mother.
Savita Halappanavar died in hospital in 2012 after being denied an abortion during a miscarriage, and in 2016, Amanda Mellet was forced to travel to England to terminate a pregnancy with a fatal foetal anomaly.
Yet the Irish Times exit poll showed overwhelming majorities in all age groups under 65 voted for change, including nearly nine in every 10 voters under the age of 24.
I am a young Irish woman.
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.More news: What Emilia Clarke Plans to Conquer Next
Chris Garvin, 20, who works in human resources, said: "I'm not going to try and sway people's opinions but it's a very, very important matter and I think it's going to affect everybody's lives in some way".
Voting has already taken place on Ireland's offshore islands.
Later today, the Republic of Ireland will hold a historic referendum on abortion rights that might finally pave the way for abortion to be decriminalised.
After that, abortions will only be allowed until the 24th week of pregnancy if there is a risk to a woman's life, or a risk of serious harm to the physical or mental health of a woman. According to several exit polls, it looks as if pro-abortion forces have decisively delivered enough votes to overturn the country's 8th amendment that bans abortion.
After previously tweeting that "the 8th amendment prevents nothing but the safety and dignity of our fellow citizens".More news: Victoria Beckham Weighs In On Meghan Markle's Royal Wedding Gown
However, some are not letting this stop them from having their say, and are travelling thousands of kilometres through multiple continents to make it back to the motherland.