The leadership of the Green Party has failed to secure enough votes from members to make support for the Lisbon Treaty referendum official party policy.
After hours of debate, a motion in favour of making support for the treaty party policy fell narrowly short of the two-thirds majority required. Some 63 per cent voted in favour of the motion.
Green Party leader and Minister for the Environment John Gormley was positive despite the narrow defeat for the motion and said the parliamentary party position had been endorsed.
"This is a historic day for the Green Party. I believe that our conception of, and approach to, Europe has been updated to reflect what our parliamentary party thinks, and what the majority of our councillors and members think.
"It is always difficult for any organisation to win a two-thirds majority on contentious issues, but I interpret today's vote as a mandate for myself and my parliamentary colleagues to recommend a yes vote in the upcoming treaty debate," Mr Gormley said.
He said the reservations of those who opposed the motion will not be overlooked.
The Greens have for many years staunchly opposed greater EU powers, with Mr Gormley often in the vanguard. However, as last year's general election approached, with the possibility of entering coalition on the horizon, it began an internal debate on taking a more practical line on Europe.
Today's vote will not close the internal debate and members, particulalrly former MEP Patricia McKenna, will be free to campaign against the treaty.