The French Socialist Party has declared Martine Aubry its new leader after a bitter leadership fight.
According to official results of last Friday's ballot issued on Tuesday, Ms Aubry won by 102 votes over former presidential candidate Segolene Royal.
Ms Aubry is a former Labour minister who introduced the 35-hour work week in France in 2000 and the daughter of former European Commission President Jacques Delors. She claimed victory at the weekend after an initial count gave her the lead by 42 votes.
However, Ms Royal demanded verification of the result, accusing her of irregularities.
The result was validated on Tuesday evening by the party's top council.
The BBC reports the process has left the party deeply divided and the French press is speculating on a possible formal split.
The Socialists are seen as unable to provide an effective opposition to President Nicolas Sarkozy.
The party has not won a presidential election since 1988 or a parliamentary election since 1997. It has 233,000 members.