Several thousand people marched through central Paris, in torrential rain, behind a banner reading "Halt the massacre in Gaza and West Bank, immediate ceasefire".
"France must immediately call for a ceasefire so that the guns go silent," said CGT union secretary general Sophie Binet, one of several union leaders to speak at the rally.
Rallies were held in dozens of towns across France, Binet added.
In Marseille, several hundred people staged a minute's silence for Palestinian victims of the aggression. In Toulouse, more than 1,200 people took part in a march, according to police.
Israel launched its relentless attacks on the besieged coastal enclave and cut off water, food, medicine, fuel and power, targeting Gaza's schools, hospitals, residences, and places of worship, after Palestinian resistance groups launched a surprise attack against the regime on October 7 in response to decades of atrocities.
Source: Agencies