The vote will decide whether to repeal a part of the constitution, known as the Eighth Amendment, which effectively bans terminations in the country, reports the BBC.
Currently, abortion is only allowed when a woman's life is at risk, but not in cases of rape, incest or fatal foetal abnormality.
Polls opened at 7 a.m. and will close at 10 p.m.
More than 3.2 million people are registered to vote in the referendum, with more than 100,000 new voters registering ahead of the poll.
The referendum is the result of a decades-long debate about abortion in Ireland and will be the country's sixth vote on the issue.
The Eighth Amendment was introduced after a referendum in 1983, the BBC reported.
The ballot paper does not mention the Eighth Amendment or abortion, instead asking: "Do you approve of the proposal to amend the Constitution contained in the undermentioned Bill?"
Counting of the votes will begin on Saturday morning, with a result expected later in the evening.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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