Marseille's top Jewish leader Zvi Ammar said Tuesday that the Or Thora synagogue has been sold, as the 250-capacity site has not been used often.
Ammar remarked that there are some 58 synagogues in the city, and local Jews have recently been moving away from the city center into the suburbs.
"For the past 20 years or so we have seen the shift of the Jewish community to other neighborhoods," he told AFP, adding that the deal should be regarded in a positive way, "We all have the same God, the main thing is for this to proceed in harmony."
The soon-to-be mosque, located not far from the Saint-Charles train station, was built after Jews traveled to Marseille from Algeria when the country gained independence from France in 1962. The city's 70,000 Jews represent one of the largest such communities in the country and in the whole of Europe.
The local Muslim community initiated the construction of a Grand Mosque back in 2001, but the project, promised by the city's mayor, faced financial hardships and legal challenges from members of the far-right National Front.
Costing about 23 million euros ($26 million) if fulfilled, it will be the largest mosque in France.
The sale of the synagogue is currently being reviewed by the city council. The new religious site is expected to be open in summer.