A 'Green wave' has swept through polling stations across the country to put the party in major contention for three European seats.
The Greens scored 9pc in an exit poll of 3,000 voters, which is a massive jump from 1.6pc five years ago.
Fine Gael and Fianna Fail are tied in terms of popular support, reducing the chances of either Leo Varadkar or Micheal Martin pushing for a general election in the near future.
Sitting Green Party councillor Ciaran Cuffe is set to top the European poll in Dublin with 23pc, which will come as a massive shock to Fine Gael, Fianna Fail and Sinn Fein.
The three largest parties are in a battle to take one of the three automatic seats with Independents4Change Clare Daly.
Former Tanaiste Frances Fitzgerald is on course to finish second in the capital on 14pc.
Fianna Fail's Barry Andrews is on 12pc alongside Ms Daly.
The only sitting MEP in Dublin running for re-election, Sinn Fein's Liadh Ni Riada, is on 10pc and at serious risk of losing her seat.
As expected, Fine Gael's Mairead McGuiness will top the poll in the Midlands-North West, with the RTE/TG4 exit polls putting her on 25pc.
Sinn Fein's Matt Carthy is likely to return to Brussels with 15pc first preferences.
However, the other sitting MEP, Luke 'Ming' Flanagan, faces a battle to retain his place.
He is on 10pc behind the Green Party's newcomer Saoirse McHugh (12pc).
Ms McGuinness' running mate, Maria Walsh, is also in contention for the fourth seat on 10pc.
Independent Peter Casey is on 7pc and could feature too.
Once again, the constituency has proved a bridge too far for Fianna Fail, who will be desperately disappointed with the showing of former minister Brendan Smith and Galway TD Anne Rabbitte. They have a combined vote of just 9pc.
Nationwide, Fianna Fail and Fine Gael picked up 23pc of the vote in the local elections, while the Green Party picked up 8pc.
In the referendum on divorce, an overwhelming majority of 87pc voted in favour of easing restrictions.
Turnout at the local and European elections and the referendum was mixed across the country.
In Dublin, it was slow for most of the day, but there were reports of up to 30pc turnout in Galway and 28pc in Kerry.
Two of the 13 elected Irish MEPs face an uncertain wait as to when they can take their seats due to the Brexit delay.
Ireland has received two of the 27 places formerly reserved for the UK, which are being redistributed among 14 member states.
However, the UK is participating in the poll, with British MEPs set to attend the inaugural plenary session of the new parliament on July 2.
As a result, those elected in last place in Ireland's Dublin and South constituencies must wait to see if they can take their seats.
President Michael D Higgins and his wife Sabina voted yesterday morning at their local polling station at St Mary's Hospital in Dublin's Phoenix Park.
Taoiseach Leo Varadkar voted at around noon at his local polling station in Castleknock.
After marking the ballot papers, he joked: "I really had to think about the transfers."
Sinn Fein leader Mary Lou McDonald voted at St Joseph's School on the Navan Road.
In Cork, Fianna Fail leader Micheal Martin was accompanied by his wife Mary and their children Micheal A and Aoibhe, as they all cast their votes at St Anthony's Boys National School in Ballinlough.
Residents on remote Atlantic islands off Donegal, Galway and Mayo cast their votes on Thursday.
Voters in Cork, Waterford and Limerick were also able to participate in plebiscites on Government proposals to create directly-elected mayors.
Counting in the local elections and divorce referendum will begin this morning.
The European election count for Ireland's three constituencies - Dublin, South and Midlands-North-West, will begin tomorrow morning at centres in Dublin, Cork and Castlebar, Co Mayo.