The Dáil has passed the Bill that allows for the referendum on the Lisbon Treaty.
Only five Sinn Féin members opposed the bill, which was passed without a vote.
The No campaign is already under way, while the Government's formal Yes campaign begins on 12 May.
The Tánaiste and incoming Taoiseach, Brian Cowen, has promised to lead a vigorous campaign in favour of the Treaty because of what he sees as its importance for the Irish people.
Ireland is the only EU member state holding a treaty referendum, which will be held on 12 June.
For more on the Lisbon Treaty go to www.rte.ie/lisbon.
