While it is true that most French identify as Catholic, or are identified as such by bureaucratic derivations, Brenus is basically correct.

From Wiki:

According to the Eurobarometer Poll conducted in 2010,[3] 27% of French citizens responded that "they believe there is a God", 33% answered that "they believe there is some sort of spirit or life force", and 40% answered that "they do not believe there is any sort of spirit, God, or life force". This makes France one of the more secular countries in the world.