Exit polling data suggested many voters in Ireland had made up their minds on abortion before the official campaign began eight weeks ago, academics said.
Only a minority were swayed by the divisive and emotive public debate around the issue over recent days.
Pollsters said people were more affected by the stories of women who have suffered due to Ireland's tight restrictions, travelling to England for the procedure or taking abortion pills obtained on the internet without supervision.
More than a year ago a public advisory body to the Irish Government voted in favour of having no restrictions on early pregnancy by a margin similar to the predicted outcome of Friday's referendum.
The Citizens' Assembly decided by 64% to 36% in favour of the momentous step.
The body is made up of 99 members chosen at random to represent the views of the Irish electorate.
It was established by the Oireachtas parliament to consider some of the most important issues facing Ireland in the future and began its meetings in 2016.
Its most controversial task was deciding whether to repeal the Eighth Amendment of the Irish Constitution - which gives an equal right to life to a pregnant woman and an unborn child, and prohibits abortion unless a woman's life is in danger.
When the Assembly returned its verdict the Government quickly promised a referendum and announced the date earlier this year, as well as its proposals for reform.
They drew on the Assembly's recommendations and draft provisions include that terminations would be freely available, subject to medical advice and a cooling-off period, up to 12 weeks, with more restricted provision from 12-24 weeks.