The Nice Treaty has been ratified by the Irish electorate with 62.89 per cent voting in favour of the amendment to the Constitution. There was a turnout of 48.5 per cent.
A Yes vote became obvious early this morning with a strong swing in favour of the treaty in the counting of the seven "electronic" constituencies. The vote was maintained in the remaining manually counted votes throughout the day.
In the Taoiseach's constituency, Dublin-Central, 57 per cent voted Yes. Mr Ahern welcomed what he described as an "emphatic Yes vote" in the referendum.
The highest vote in favour was in the Dublin constituency of Dun Laoghaire, where 73.9 per cent voted Yes.
The turnout was significantly ahead of the last poll with overall turnout of 48.5 per cent compared to 35 per cent last year.
The Fine Gael leader Mr Enda Kenny said Ireland's Yes to Nice is an "historic decision for democracy and for the future of Europe."
"Ireland's YES proves the sophistication of the electorate," he added.
The President of the European Parliament Mr Pat Cox said the Irish electorate had "removed the last brick of the Berlin wall".
He described the ratification of the treaty as "a good result for Ireland and good result for Europe".
European Commission president Mr Romano Prodi hailed the results, saying the Yes vote exceeded expectations.
Speaking on French radio station Europe 1, Mr Prodi said: "The indication is even better than expected. Ireland is giving a green light to enlargement."