Sinn Fein has won 13 seats in the Irish general election, a gain of eight on its representation in the last Dail.
Party president Gerry Adams topped the poll in Louth, winning a seat on the first count.
While many analysts predicted his victory, the party has surpassed expectations in other constituencies.
BBC NI election analyst Gerry Lynch said the election of Sandra McLellan in Cork East was the most surprising of the whole election so far.
He added that Sinn Fein was likely to pick up another seat in Laois-Offaly and had a fifty-fifty chance of winning in Wicklow.
The party has rebounded from a relatively poor performance in the 2007 election when its representation went from five to four.
However, the victory of Pearse Doherty in Donegal SE in a by-election at the end of last year has heralded a much stronger performance this time.
Mr Adams said that Sinn Fein had been rewarded for its hard work on the ground during the campaign.
"We went out in this election, we set out our stall very, very clearly," he said.
"I think the votes across the state show a significant amount of people support the position we have taken up."
The Northern Ireland deputy first minister Martin McGuinness said the performance was a sign of a shift in Irish politics.
"This election is a step-change for Sinn Fein because we have a number of rising stars in our party, who are very republican, who are very conscious of the need to put people first," he said.
"So the blend of experience, and the coming to the fore of these young people, I think is going to be very powerful in the course of the next Dail."
Mr McGuinness also paid tribute to his party leader Mr Adams, congratulating him on his win in Louth.
"It will be very powerful for Sinn Fein to see the leader of our party being elected, and effectively being full-time in the south.
"(It) is of huge importance because all of that undoubtedly complements the strides forward we have taken in the north."