While the French Council of the Muslim Faith (CFCM) initially insisted Ramadan began today (9th), the theological council at the Great Mosque of Paris argued it would not start until tomorrow (10th).
The later date is the day many Arab countries are due to begin the observance.
However, the CFCM later reversed its decision.
It said in a statement that "in order to preserve the unity of French Muslims," it had joined the mosque in declaring tomorrow the start of Ramadan.
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The CFCM decided in May that today would represent the start of Ramadan based on the expected arrival of the new moon.
Theologians, however, at the Paris mosque decided on yesterday night to put the start off by a day, saying the new moon had not been sighted.
"Mosques were calling us yesterday until 1:00 am, the imams were in disarray," said Djelloul Seddiki, the head of the mosque's theological council.
Dalil Boubakeur, who is both the president of the CFCM and rector of the Paris mosque, said the change in date followed an outcry in the community that Ramadan was not starting in France on the same day as in many Muslim countries.
He said the confusion had been "a lesson" for French Muslim leaders and that it would be legitimate to start observing Ramadan on either day.
The confusion mirrored differences elsewhere across the Muslim world as Sunnis and Shiites began the holy period at different times.
During Ramadan, Muslims are also required to abstain from drinking liquids, smoking and having sex from dawn until dusk.
Fasting is one of the five main religious obligations under Islam.