First estimates of an internal poll held by the French Socialist party on the evening of 1 December have indicated a strong backing for the EU's Constitutional Treaty.
After 85% of votes had been counted last night, the 'oui' had 59.07% of the vote with 40.93% going to the 'non', François Rebsamen, number three in the Socialist party, indicated to Reuters.
Definitive results will not be known until all of the 3,700 sections of the Socialist Party (PS) send in their ballot, Rebsamen said, but "the difference was such that the tendency could not be reversed now".
Turnout was high with about 95,000 out of the 120,000 card-carrying members showing up, or a turnout rate of 79%, said Rebsamen.
"This is a lesson of democracy for France and for Europe," he added in a sign already interpreted by French observers as a gesture of reconciliation directed at the defeated 'non' camp.
The French Socialists' position on the Constitution was considered crucial in the national referendum to be held in 2005. The fact that the party had won all but one constituency at the regional elections in June had made it arguably the dominant party in French politics.
The question now is whether and how the winning 'oui' camp will square off with the defeated 'non' camp after a bitter campaign that left the Socialist Party deeply divided.
"Reconciliation is possible. In a way, it is in our genes," Claude Bartolone, a close ally of Laurent Fabius and a supporter of the 'non' told the French news channel LCI.
In a statement, the leader of the 'non' camp, Laurent Fabius, said he took note of the result of the ballot "with regret" and affirmed his "attachment to the unity" of the Socialist Party.