With a turnout of 49 per cent, Cllr Nulty is on 24.3 per cent (8,491 votes) after 100 per cent of tallies have been counted.
While there has been no official count yet, the councillor (28), who works for a homeless charity, has already been congratulated by party colleagues and opponents.
Fianna Fáil Cllr David McGuinness has 21.7 per cent of the tallies with an estimated 7,575 votes, while Socialist party Cllr Ruth Coppinger is in third place with 21 per cent (7,337 votes) and Fine Gael Cllr Eithne Loftus is trailing in fourth place with 14.8 per cent (5,167 votes) - down on the party’s 27.9 per cent showing in the general election.
Sinn Féin candidate Paul Donnelly is on 9 per cent based on the tallies with 3,128 votes, up almost 3 per cent on his showing in February.
Green party candidate Roderic O’Gorman polled about 5 per cent of the votes (1,759), well up on his poor 1.42 per cent general election result.
Fine Gael director of elections and Minister of State Brian Hayes conceded it was a “disappointing result" for the party. "Labour are going to win which will be an extraordinary achievement for them, given that a Government candidate has not won a byelection since 1982 [when Noel Treacy won the Galway East byelection]" he said.
“At the end of the day this is a local contest, and I don’t see this as a permanent decline for Fine Gael, but we as a party locally and nationally need to work out what went wrong.”
The first count result is expected at about 2pm in the poll of 13 candidates.
Fianna Fáil party members are delighted with their candidate’s performance in the election, particularly polling ahead of Fine Gael. One senior party member said: “We’re not breaking out the champagne yet, but we are back in the game”, after the drubbing the party got in the general election.
However, if the tallies pan out into the actual count it leaves Fianna Fáil without a single TD in the Dublin area, following the death of former minister for finance Brian Lenihan. In the general election, Cllr McGuinness, Mr Lenihan’s running mate, polled just 623 votes, while the party, with two candidates then, had 16.59 per cent.
Cllr Nulty came fifth in the four-seat constituency in the general election and was the last to be eliminated in that contest, when he and running mate and poll topper Joan Burton garnered 29 per cent of the vote between the