Michael D Higgins will be Ireland's ninth president after one of the most remarkable political comebacks in the history of the state.
The Labour Party veteran, poet and campaigner, seized an unprecedented swing in support following the spectacular implosion of his biggest rival on live television.
Mr Higgins declared his triumph was built on a left-leaning campaign while his seven-year term will be marked by inclusion, ideas and transformation.
The 70-year-old's resounding victory was obvious within an hour of ballot boxes being opened in a massive voter swing just days after favourite Sean Gallagher publicly derailed during a TV debate.
"I feel a little overwhelmed," Mr Higgins said. "I'm very, very happy. It is something I prepared for, something I thought about for a long while. I am very glad as well that it is a presidency built on a campaign that emphasised ideas. I hope it will be a presidency that will enable everybody to be part of and proud of."
Mr Higgins secured the victory for Labour - the second in a day as the party edged towards a by-election win - after the other six candidates conceded defeat. He took 40% of the poll, 701,101 votes out of 1,77 million, on the first count.
Mr Gallagher, the opinion poll topper with a 15-point margin as recent as Sunday, saw his support vanish to 28% in a stunning defeat blamed on his ties to Fianna Fail, the party most associated with Ireland's economic demise. But the businessman refused to criticise. "These are campaigns and this is the nature of a campaign," the former political fund raiser said.
Mr Higgins will be inaugurated on Armistice Day, November 11, the day after current president Mary McAleese leaves office.
Runner-up Mr Gallagher would not blame the man who derailed his seemingly unassailable campaign on live TV last Monday. The businessman - a former fund raiser for the Fianna Fail party which was widely blamed for the country's economic woes - ran into a storm of controversy amid allegations he was a "bag man" soliciting and collecting donations.
Sinn Fein's Martin McGuinness, who was ran third in the poll securing a tactical victory, dropped the bombshell that Mr Gallagher had requested and personally received a 5,000 euro (£4,390) cheque from a businessman with a conviction for tax fraud and fuel smuggling.