Pearse Doherty has been elected in the Donegal South West by-election to fill the Dáil seat vacated by MEP Pat The Cope Gallagher.
He was elected after the fourth count without reaching the quota. Fine Gael's Brian O'Neill came second with Fianna Fáil's Brian Ó'Domhall in third place. The total valid poll was 34,424 and the quota is 17,213.
Mr Doherty got the highest number of first preference votes with 13,719 in the first count.
He described the election as, 'the by-election the Government never wanted to happen' adding that 'the result tells us why'.
Speaking after the result was announced, Mr Doherty said the vote was a rejection of the interference of the IMF in Irish affairs and said he would be voting against the Budget on 7 December.
Independent Ann Sweeney was excluded after the first count, Frank McBrearty of Labour was excluded after the second count and Thomas Pringle (Independent) was eliminated in the third count.
Sinn Féin has moved to capitalise on its victory with an approach to Independent TDs to discuss the formation of a technical group in the Dáil to give it more speaking time.
It is believed that the party has contacted Dublin North Central Independent Finian McGrath to open discussions on the move, which would allow the party to move a no confidence motion in the Government.
It is understood Deputy McGrath will discuss the appraoch with fellow Independent Maureen O'Sullivan over the weekend, before talks with Sinn Féin next week.
If agreed, the group of seven TDs would be entitled to extra speaking time in the Dáil, and Sinn Féin would also be able to move its motion of no confidence in the Government.
There are tactical arguments against such a move, as it may encourage Government TDs to close ranks, but it would certainly put pressure on the Government - and on the other Opposition parties.
Meanwhile, Fine Gael leader Enda Kenny praised the performance of the party's candidate in his first Dáil election campaign.
Mr Kenny said Barry O’Neill was a strong candidate who has built a base of support which gives him an excellent chance of winning a seat in the coming General Election.
He also congratulated Mr Doherty and said the country needs to ‘the voices of all its people heard through a General Election which would give a new government a mandate to address the current economic climate.’
Turnout was estimated at 56%.
Traditionally, Donegal South West has been a Fianna Fáil stronghold, with the party returning two TDs in the 2007 election.
However, the political landscape is very different now and recent polls indicated Sinn Féin would perform well.