The spokesman for Ireland's anti-abortion campaign Save The 8th, has conceded his side has lost the referendum as early polling data suggests 7 out of 10 voters backed reform.
In a statement, 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 statement came as counting got under way in Ireland's historic abortion referendum. At the Royal Dublin Society, where counting started at 9am, the mood in the Yes camp was of exhausted jubilance, and as news of Save The 8th's statement, cheers echoed around the hall.
Reacting to the exit polls on Friday night, Taoiseach Leo Varadkar, a vocal proponent of liberalisation, tweeted: "It's looking like we will make history."
On Saturday, as the scale of the victory began to emerge, Varadkar tweeted the landslide vote to repeal in his own constituency of Dublin West.
In Dublin Central, 92% of people voted to repeal the eight amendment, which currently ensures abortions are banned unless a woman's life is in immediate danger.
One poll by national broadcaster RTE suggested around 70% of the electorate have voted to end the country's all but blanket ban on terminations, with another, by The Irish Times, recording 68% in favour of ditching the prohibition.
Colm O'Gorman, executive director of Amnesty International, said he hoped Saturday would be a huge milestone for women's rights. "It looks like the people of Ireland have resoundingly voted to end the 35-year-old constitutional abortion ban.
"In this, Ireland will send a powerful message to women and girls in Ireland and across the globe that their human rights and reproductive health matter.
"That women should be treated with dignity, equality, respect and compassion."
The likely result paves the way for a change in Ireland's legislation on abortion, and speaking on Saturday, the head of the Irish opposition, Michael Martin, said his party would not stand in the way of relaxing the laws.
Pundits had suggested his party's supporters were almost evenly split between Yes and No, and many of his party members in the Dail parliament advocated a No vote. He said the Dail would have to honour the will of the people.