Green Party candidate Joe O’Brien has been elected as a TD after topping the poll in Dublin Fingal.
Mr O'Brien received 12,315 votes after the eighth count to secure the first ever by-election win for his party.
Fianna Fail’s Lorraine Clifford Lee came in second with 7,754 votes.
Duncan Smith of Labour was eliminated after the seventh count into third place.
Mr O’Brien had received 22.9%, of first preference votes, followed by 18.5% for Ms Clifford Lee and 15.2% for Mr Smith.
Gemma O’Doherty, who had also contested the recent European elections and the 2018 Presidential election, was eliminated after the third count.
Turnout in the constituency was a new record low of 25.59%.
Mr O’Brien will now replace Clare Daly as TD for the constituency after she was elected as a member of the European Parliament in May.
He was the fourth and final candidate to be elected this evening.
Mr O’Brien said today’s result was it was a collective effort in Dublin Fingal and that it was more than just a ‘Green wave’.
He said: “Electoral politics can be deceiving, one person stands in front of the media like this but there was a big team behind me, we had a lot of people out on the grounds, we had a lot of people in HQ, my family in the background as well.
“It was more than just a wave, there was some serious hard work being done and a lot of people convinced on the doors as well.
Green Party chairman Roderic O'Gorman said the result indicated that the momentum gathered in May had carried on.
He said: “[It shows] that the issues we are highlighting both local quality of life issues and but also global issues about the climate crisis are still resonating with people.”
Meanwhile, the Minister for Communications, Climate Action and Environment Richard Bruton earlier played down the significance of the Green vote in Dublin Fingal.
He said: “I think by-elections have pretty much thrown up this sort of pattern forever so I think it would be a mistake to read too much into elections were less than one in five have turned out to vote.”