Some 67.1% of those who voted in the second Lisbon Treaty referendum yesterday cast their ballots in favour of the EU reform package, according to today's official result.
Voters on the 'Yes' side stood at 1,214,268, with 594,606 opposed.
Turnout across the country stood at 59%, according to the Referendum Returning Officer.
Taoiseach Brian Cowen said the result was a declaration of intent to stay at the heart of Europe.
Mr Cowen said: “It is a good day for Ireland, it is a good day for Europe.”
The Taoiseach refused to be drawn on the scale of damage to Ireland's reputation from last year's defeat and how much work was needed to restore its standing with EU neighbours.
“To the question of what damage was done at that time to the Irish, I think there was respect for the democratic process and the fact that it couldn’t be overturned without returning to the democratic process,” Mr Cowen said.
Mr Cowen said legal guarantees hammered out earlier this year helped public opinion swing towards a Yes, but accepted the economic threat of distancing the country from Europe played a key role in the run-up to the ballot.
“What’s important to point out is that Ireland has always been a core Euro-positive country,” he said.
“It is a country that acknowledges, recognises and appreciates the benefits that membership has brought.”
Fine Gael leader Enda Kenny called the vote a "mature" and "informed" decision.
“Yesterday, the Irish people stepped up to the mark and made a very positive decision for our country’s future," Mr Kenny said.
"Through this decisive result, Ireland has strengthened its place at the heart of the European family."
Green Party leader and Environment Minister John Gormley said the result "removes any uncertainty about Ireland's relationship with the European Union: we are committed and progressive members and we will continue to occupy a key role in the EU".
Energy Minister Eamon Ryan said: "I think this day will be seen as a turning point in years to come – the day we decided to come together and face our future in a spirit of solidarity.
"The problems we face have not gone away, but we can use this as a new beginning as we set to work on our recovery," Minister Ryan said.
"By joining and working with our European neighbours we have a greater chance of success in tackling our major challenges. In a time of crisis you can turn inwards and divide, or you can look outwards and unite. Today we made the positive choice."
More than 1.2 million people voted in favour of the treaty this time round – a 20% swing since the shock rejection last year.
Only the two Donegal constituencies on the north-west tip of Ireland said “no” on this occasion.
European Commission president Jose Manuel Barroso spoke by phone to the Taoiseach to congratulate him on the result.
Sporting a carefully-chosen green tie, Mr Barroso welcomed the resounding win from Brussels.
“The Irish people have spoken. They have said a resounding Yes to Europe. Thank you Ireland. It is a great day both for Ireland and for Europe,” Mr Barroso said.
Prime Minister Gordon Brown also welcomed the emphatic result.
Only Poland, which is expected to rubber stamp the treaty within days, and the Czech Republic, where there is a legal challenge, have yet to formally ratify the reform deal.
The last 15 months saw a massive turnaround in public opinion following assurances from Brussels on the key concerns of Irish people – tax, neutrality, abortion and retaining a Commissioner.
But worries over the economy also formed a decisive part of campaigning over the last four weeks.
Multi-millionaire businessman and unsuccessful European candidate Declan Ganley claimed voters had made a mistake and branded the “yes” campaign dishonest.
“I’d like to say it was inspired by hope but I fear that it was not, but I respect the outcome,” Mr Ganley said after his second attempt to derail EU reform failed.
Asked about campaigning “scare tactics”, Mr Barroso responded: “Any campaign of fear was generated by the No campaign, with tactics such as posters about a minimum salary being imposed on Ireland by Europe.”
Despite seething anger at the coalition Government over Ireland’s property crash, banking crisis and subsequent recession, opposition politicians claimed voters put distrust behind them to act in the national interest.
Labour leader Eamon Gilmore seized on the opportunity declaring: “The national interest now requires that this Fianna Fail government be removed from office as quickly as possible.”
The “no” camp – which included a array of activists from Socialist MEP Joe Higgins to the UK Independence Party, Sinn Féin and lobby group Cóir – demanded the Government deliver on commitments that Lisbon will deliver jobs.
The Lisbon Treaty, born out of the rejected European Constitution, was billed as reform to streamline decision making in Brussels.
It will create a president of Europe, an EU foreign minister, reduce a state’s ability to veto and increase powers in the Commission.
One of the most emotive issues in the campaign was sparked by posters from lobby group Coir, which suggested Ireland’s minimum wage would be slashed by the reform package to as low as €1.84.