Should a yes vote prevail on the 25th May, it will enable the government to legislate for allowing access to abortion.
Thousands of Irish emigrants, including people on both sides of the debate, are expected to travel home for the referendum, which does not allow postal votes from outside the country and requires returning voters to have been living overseas for less than 18 months.
"It's a rather unbelievable situation that we're going into the constitution to remove a right and we're actually going in there to remove the fundamental right to life from all unborn children". And parties may let some of their members oppose their own legislation because of the moral issues.
Irish abortion activists exploited Savita's case and lied about her death, culminating in Friday's vote.
Prime Minister Leo Varadkar called the result the culmination of a “quiet revolution.”
Sorry, this content isn't available on your device. The impact of Brexit on women's ability to travel freely remains unknown.
Vera Rooney voted against repeal. It has left Ireland with some of the most restrictive abortion laws in the world, which have been regularly criticised by a number of global human rights bodies.
"Not taking anything for granted of course, but quietly confident - there's been good turnout across the country so far and hoping for a Yes vote tomorrow. I believe God is the giver of life", the 78-year-old said, adding that he credits God with helping him overcome alcohol addiction.
He urged voters not to be distracted by the sunny weather and exercise their democratic right. It legalized divorce by a razor-thin majority only in 1995, but three years ago became the first country in the world to adopt gay marriage by popular vote.
Irish voters will decide on Friday whether to end the country's ban on abortion in most cases.More news: White House team to go to Singapore for summit preparation
Her photograph showed her proudly posing with her passport with a cheeky grin on her face. In March, supporters of the pro-life campaign marched on the streets of the capital, vowing that life starts at conception.
John McGuirk, spokesman for the Save the 8th group, told Irish television Saturday that many Irish citizens will not recognize the country they are waking up in.
"A lot of unborn children will lose their lives in the future, that's what happens when abortion gets legalised", Mr Mullen said.
"We're all aware of the various cases where women have died because they haven't been able to access appropriate medical treatment for a spontaneous miscarriage because of the Eighth Amendment".
Many people are genuinely undecided about the referendum. It was not until the tragic death, on 28th October 2012, of Savita Halappanavar, that legislation regulating life-saving abortions was introduced.
Opinion polls have been tight, with most showing the Yes side in the lead. The companies said concerns were raised about influence from unknown sources.More news: Census: Chicago's population drops 3rd year in a row
But Friday's vote looks set to be closer.
Voters were asked whether they wanted to keep or repeal the Eighth Amendment to Ireland's Constitution, which requires authorities to treat a fetus and its mother as equals under the law.
In recent weeks, the lead of the "Yes" side - to repeal the so-called Eighth Amendment in the Constitution that gives equal rights to a pregnant woman and her unborn child, effectively prohibiting abortion unless a woman's life is at risk - has shrunk.
For many opponents, abortion amounts to murder, while others worry Ireland is losing its identity as a Catholic country.
Terminations would also be permitted in cases of fatal foetal abnormality.
In 2013, legislation was amended to allow terminations under certain tightly restricted circumstances - the Protection of Life During Pregnancy Act. Flávia Simas of Migrant and Ethnic-minorities for Reproductive Justice (MERJ) explained the discriminatory impact of the Eight Amendment on migrants in Direct Provision, reminding us of the harrowing case of Ms Y, an asylum seeker, pregnant as a result of rape and suicidal, who was denied an abortion in 2014.More news: White House adviser Kushner's permanent security clearance restored
Under pressure from the United Nations about alleged degrading treatment of women who travelled to England for terminations, the Irish Government began exploring the possibility of further reform, culminating in the calling of this referendum and the promise to legislate.