Official referendum figures declared at the Dublin Castle count centre showed the controversial pact was backed by 60.3% of those who voted.
The country's backing for Europe's fiscal pact eased stress levels in Brussels, with eurocrats welcoming a glimmer of good news in the midst of gathering economic gloom.
Although an Irish No would not have derailed the new pact – only 12 out of 17 eurozone countries need to ratify it – it would have been seen as a thumbs down to the European Union and a boost to eurosceptics.
One EU official said: "A No vote was the last thing anyone needed at this time."
Twenty-five of the EU's 27 member states have signed a landmark treaty to co-ordinate their budget policies and impose penalties on rule-breakers – the "fiscal compact". Rejecting the pact – which sets debt and deficit reduction targets with penalties for breaches – would have blocked Ireland from any further emergency EU funding following its €85 billion (£68bn) bailout from the EU and IMF.
Five of Ireland's 43 constituencies rejected the plan, including both electoral regions of Donegal and three others in Dublin, one of which is home to two ministers.
But returning officer Riona Ni Flanghaile announced a total of 955,091 votes in favour compared with 629,088 against the agreement.
European Commission President Jose Manuel Barroso later described the pact as "a key component of the EU's response to the current economic crisis".
In a statement welcoming the result, he said: "Restoring sustainability to public finances remains an important objective.
"I know that many voiced their concerns about the need for growth during the campaign.
"The European Commission believes that stability and growth go together and that we cannot have one without the other. The Commission will continue to build on its agenda for structural reform and targeted investment to boost growth."
He added: "Earlier this week we published proposals designed to get the EU growing again which we hope will be strongly supported in Ireland.
"Ireland has established a strong track record in implementing its EU/IMF financial programme. Today's vote represents a significant step towards Ireland's economic recovery and its place at the heart of the EU."
It came as worrying signs that eurozone woes are contaminating powerhouse economies in the US and China triggered another slide on world markets.
The weakest US jobs growth in a year, and figures showing expansion in China's manufacturing sector almost halted last month, dashed hopes that the world's two largest economies will ride out the euro storm.
The wave of grim data knocked more than 1% off London's leading shares index, which endured its worst month in three years in May. The Dow Jones Industrial Average was off 1.5% following the latest jobs figures, while declines were even heavier on markets in Germany and France.
The pound slipped lower on currency markets as the weak UK manufacturing data made it more likely that the Bank of England will be forced to restart its money-printing programme to boost the economy.
In Ireland, Sinn Fein President Gerry Adams warned the Government will be tackled harder now on whether it can meet commitments to ease the pressure of austerity.
"The Government has given firm commitments in terms of committing on a bank bailout, in terms of growth and jobs incentive initiatives, so we will be holding the Government to those promises," he said.
In his first response to the resounding victory, Taoiseach Enda Kenny said Ireland's bank debt must be included in future discussions to revive the wider European economy.
"The Irish people have sent a powerful signal around the world that this is a country serious about overcoming our economic challenges," he said.
"The treaty will not solve all economic problems but it is a foundation stone to make sure the economy stands on firm ground."
But UK Independence Party leader Nigel Farage said: "The Irish political class has continued to persuade the people of Ireland to give up their hard-fought and short-lived independence."
