Sinn Fein have picked up 21.1% of the vote, with Fine Gael on 21% and Fianna Fail on 19.5%, the poll by RTE, The Irish Times, TG4, Trinity College Dublin and Ipsos B&A suggests.
The poll has a margin of error of 1.4% and was published after voting ended at 10pm on Friday.
While the exit poll is a good indicator of how well each party has done, how many seats they will pick up is still unclear due to Ireland’s electoral system.
Voters in Ireland rank their choices rather than choosing one candidate. Prospective politicians must then reach a quota after rounds of vote counting, with between three and five seats up for grabs in each constituency.
Explainer: How Ireland’s election voting system works
Fine Gael’s Simon Harris, Fianna Fail’s Micheal Martin and Sinn Fein’s Mary Lou McDonald are all in contention to become Ireland’s next taoiseach.
A coalition is inevitable as no party has put forward enough candidates to win a majority.
But Sinn Fein’s vote share may not translate into enough seats to be in a strong position to form a government – meaning a Fine Gael-Fianna Fail coalition is likely, along with other parties.
Mr Martin and and Mr Harris have vowed not to join a coalition with Sinn Fein, which has never been in government.
Meanwhile, the Green Party is on 4% in the exit poll, Labour on 5%, the Social Democrats on 5.8% and Solidarity-People Before Profit on 3.1%.
Independent candidates are on 14.6%, Aontu is on 3.6% and Independent Ireland has 2.2%.
Fianna Fail and Fine Gael fare better on second preferences in the exit poll, gaining 20% each, with Sinn Fein picking up 17%.
The exit poll is based on 5,018 completed interviews conducted immediately after people voted at polling stations in 43 constituencies across the country.
The three-week campaign – though largely uneventful – saw support for the three main parties narrow within a few percentage points of each other.
Read more: How Trump looms over Ireland’s election
Sinn Fein, for years seen as a government in waiting, saw their longstanding lead in opinion polls plummet before the election after internal party scandals and an unclear stance on immigration.
But the party climbed back into contention, with Fianna Fail’s support remaining steady.
Fine Gael’s popularity appeared to slump over the campaign after a damaging video emerged of Mr Harris appearing to dismiss a voter’s concerns about disability care.
Almost 700 candidates are contesting the election. It may take days for all 174 seats in the Dail, Ireland’s lower house of parliament, to be filled – and even longer to form a coalition.
It took almost five months after the 2020 election for the last coalition government to be established – though the COVID pandemic impacted negotiations.
In that election, Sinn Fein won the highest vote percentage with 24.5% – translating into 37 seats.
But Fianna Fail was the largest party with 38 seats on 22.2%. Fine Gael won 35 seats with 20.9%.