- Video report from ITV News Social Affairs Editor Penny Marshall
Yes campaigners hailed a "resounding" victory as Ireland voted overwhelmingly to change its restrictive abortion laws.
Irish Taoiseach Leo Varadkar said that a "quiet revolution" had taken place, as voters chose to repeal the Eight Amendment.
He added that the outcome proves Ireland "trusts and respects women to make their own decision and choices."
Shortly after counting begun on Saturday, a lead anti-abortion group, Save the 8th, conceded defeat.
Final results showed that 66.4% of voters backed reform, with 33.6% against.
Mr Varadkar said: "The public have spoken, the result appears to be resounding in favour of repealing the Eighth Amendment, possibly to carry every constituency in the country."
In a statement, Save the 8th communications director John McGuirk said: "The unborn child no longer has a right to life recognised by the Irish state.
"Shortly, legislation will be introduced that will allow babies to be killed in our country. We will oppose that legislation."
The landslide in favour of liberalising abortion laws in the Irish Republic has now prompted fresh calls for similar action north of the border.
Northern Ireland will soon become the only part of Britain and Ireland where terminations are all but outlawed.
There were reports of strong turnout in many parts of the country, particularly in urban areas.
Thousands of Irish citizens living overseas have travelled home in droves to exercise their democratic right on the emotive issue.
The Irish Government intends to legislate by the end of the year to make it relatively easy for a woman to obtain the procedure in early pregnancy.
Ministers have promised to allow terminations within the first 12 weeks, subject to medical advice and a cooling-off period, and between 12 and 24 weeks in exceptional circumstances.
Since 1983, the now-repealed Eighth Amendment had forced women seeking to terminate pregnancies to go abroad for abortions, bear children conceived through rape or incest or take illegal measures at home.
President Michael D Higgins and his wife Sabina cast their votes in Dublin on Friday morning.
Around two hours later Taoiseach Leo Varadkar, a vocal advocate for repeal, voted in the city.
“I always get a little buzz from voting, it just feels like it is democracy in action,” Mr Varadkar said after emerging from the polling station at Castleknock.
“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.
“Obviously, I would be encouraging everyone to come out and vote, a high turnout would be to the advantage of the yes campaign.”
He urged voters not to be distracted by the sunny weather and exercise their democratic right.
Leader of the main opposition party, Fianna Fail’s Micheal Martin, voted to repeal in his constituency in Cork while Sinn Fein President Mary Lou McDonald also cast a Yes vote in Dublin.
However, her Sinn Fein party colleague and vocal anti-abortion campaigner Peadar Toibin called on Irish people to vote No to “abortion on demand”.
“The irony that the referendum on abortion is being held on International Missing Children’s Day will not be lost on many Irish people,” he tweeted.
“Those on the margins of society suffer most from abortion. Vote No to Abortion on Demand.”
The Catholic Church was among the influential voices arguing that the life of the unborn should be sacrosanct, but the retain campaign faced a major challenge from the Yes camp which has portrayed itself as modernising and in step with international opinion.
The debate during eight weeks of campaigning was divisive, with the leaders of all the main political parties, including Fine Gael leader Mr Varadkar, backing change.
They argued that a Yes vote represented the compassionate choice for thousands of Irish women forced to travel to England for the procedure.
Opposing them was a vocal No camp, including the bishops, which insisted the life of the child is sacrosanct and interference in that right is immoral.
Campaigners against change used emotive language to highlight the threat to the foetus and warned against “extreme” proposals from the Government which could be expanded in future years.
They have said they will oppose the new legislation.
The Eighth Amendment is a clause in the constitution which was written after a previous referendum on the issue in 1983 recognised the right to life of the unborn child.
Its intention was to protect the equal right to life of the mother and the unborn and effectively prohibits abortion in most cases.
In 1992, women were officially given the right to travel abroad, mostly to the UK, to obtain terminations. Pro-repeal campaigners said almost 170,000 have done so.
The liberalisation campaign gathered momentum after an Indian dentist, Savita Halappanavar, died in hospital in Galway aged 31 when she was refused an abortion during a miscarriage.
Her husband, Praveen Halappanavar, said she repeatedly asked for a termination but was refused because there was a foetal heartbeat.
In 2013, legislation was amended to allow terminations under certain tightly restricted circumstances – the Protection of Life During Pregnancy Act.
When doctors felt a woman’s life was at risk due to complications from the pregnancy, or from suicide, they were permitted to carry out an abortion.
Under pressure from the UN 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.