The treaty, which sets strict new budget rules, was passed with a resounding majority of 955,091 to 629,088.
Taoiseach Enda Kenny led the Yes campaign with Fine Gael, while Sinn Féin president Gerry Adams was a figurehead in the anti-treaty camp.
Five of the 43 constituencies rejected the plan including both electoral regions in Donegal and three others in Dublin.
Mr 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."
The Taoiseach said the result would help bring stability and credibility and ensure Ireland has access to funding under the European Stability Mechanism (ESM) if needed.
Tánaiste Eamon Gilmore also said the country now needs a deal on its bank debt. His Dun Laoghaire constituency south of Dublin saw the second highest support for the treaty.
"I think this decision taken by the Irish people is a necessary step on the road to recovery but we now have to build on it," he said.
"This was not just an exercise ... asking people to vote Yes - it was also an occasion where we listened to what people were saying."
He added: "We do need to have a deal in relation to our bank debt. We do need to see progress upon it."
Sinn Féin president Gerry Adams warned that 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.
"The problems which are facing people today will be there tomorrow.
"Clearly an element of the Yes vote was ideologically committed to the Yes camp and others did so very, very reluctantly."
UTV's political editor Ken Reid said it was a comfortable victory in the end for the Yes campaigners.
"The result was immediately welcomed by the Taoiseach Enda Kenny. Gerry Adams, in the No campaign, said he accepted the result but he said that he would continue to fight for the disadvantaged," he added.
The Sinn Féin president said the campaign wasn't about them, Ken Reid explained.
"But, the reality is that this was a very good campaign for his party. They've had a very high profile - it's up to 24% in the opinion polls and although the No campaign have lost, I think Sinn Fein will look back on this as a very productive period.
Earlier, Tipperary South and Galway East declared an overall 62% majority in favour while Limerick City was 61% in favour; Tipperary North 66%; Waterford 58% and Kildare North 65%.
Ireland will now be the fourth country in the European Union to ratify strict new rules to rein in budget spending and set the groundwork for future bailout mechanisms in the Eurozone.
Polls in the run-up to the referendum had predicted safe passage for the pact with a 60-40 majority, despite a low turnout that saw half the electorate taking part.
The Republic of Ireland was the only country to give the public a say on the pact aimed at imposing more economic discipline on Eurozone states.
The fiscal pact has already been accepted by 25 of 27 member states, with the exceptions of the United Kingdom and Czech Republic.
Some 3.1m people were eligible to cast their vote but low turnouts were reported at poll stations across the Republic.
The average in Dublin was 38% while north western counties averaged around 20%.
A similar pattern was recorded in Co Cork - where the percentage later picked up - and across western and midland counties. There were a few higher results in parts of Limerick.