Why? I thought they voted NO earlier this year!
All 27 member states must ratify the Treaty before it comes into force. Ireland, Poland and the Czech Republic are the only nations that have not yet agreed to do so.
British voters were initially promised a referendum on whether to adopt the EU Constitution, but the Government decided against allowing it after the document was rebranded as the Lisbon Treaty.
On Thursday the Irish Prime Minister Brian Cowen will confirm that a new vote will be held in 2009.
Diplomats have named October as the most likely date for the vote, while Government sources said April was also being considered
Mr Cowen said he believed that the economic crisis could help persuade some of those who voted against the Treaty to change their minds.
The Government is expected to argue that Ireland would have been in a worse position if it had not signed up to the euro, and that the Treaty will speed up decision-making and help tackle the downturn.
Diplomats said a deal had been struck between France, which holds the rotating EU presidency, Ireland and EU legal services in Brussels under which the Lisbon Treaty could enter into force by January 2010.
As part of the deal, Dublin will retain the right to name an EU Commissioner – a major concession to appease Irish voters who rejected the Treaty in June. Under the treaty, the number of commissioners is to be capped at two-thirds the number of member states, each of whom currently appoint a candidate to the post.
Mr Cowen will also seek assurances from his EU peers at the summit on December 11 and 12 that the Treaty will not undermine Ireland's own policies in sensitive areas such as abortion, taxation and military neutrality, diplomats said.
"There is still some tweaking to do, but there is an understanding," a second diplomat said.
An Irish parliamentary report last month gave the legal go-ahead for the government to hold a second plebiscite.
But despite the backing of France for the special treatment Ireland is seeking in return for holding a second vote, it is far from certain that other EU states will give their blessing.