The result of the referendum is not expected until this afternoon, though opinion polls before the vote had put Ireland on course to comfortably back the treaty.
Ireland is the only Eurozone nation to have given its voters a say on the austerity pact.
Major political parties Fine Gael and Fianna Fail lobbied hard for a “yes” vote, warning that Ireland could be cut off from the new European Stability Mechanism bailout fund if it votes against it.
Ireland has given the thumbs down to two recent Eurozone referenda, though voters later supported the measures when politicians called a second poll. On occasions when the “no” vote has won, turnout has been low.
Taoiseach Enda Kenny urged the Irish to back the treaty when he cast his vote yesterday morning.