Several thousand people demonstrated in Paris on Saturday under the rallying cry "Stop the massacre in Gaza".
The left-wing organisers called for France to "demand an immediate ceasefire" between Israel and Hamas militants.
"I came to support the Palestinian cause, for a ceasefire in Gaza," said engineer Ahlem Triki, a Palestinian flag over her shoulders.
Hamas's shock October 7 attack killed about 1,200 people, mostly civilians, in Israel and 239 people taken hostage, according to Israeli officials.
The Israeli air and ground military campaign in response has left more than 11,000 people in Gaza dead, according to the Hamas-run health ministry.
"It is elementary that as activists or simple citizens, you go out on to the street to support the Palestinian people," said 85-year-old trade unionist Claude Marill.
French MPs Mathilde Panot and Eric Coquerel, whose hard-left France Unbowed (LFI) party has come under fire for an ambiguous stance on anti-Semitism, were present at the march.
Gaza ceasefire rallies also took place in other French towns including Marseille, Toulouse, Rennes and Bordeaux.
"This mobilisation is essential, in the face of massacres," said LFI coordinator Manuel Bompard at the demonstration of about 1,300 people in Marseille.
In Lyon, a Palestinian event promoting two books by a surgeon who regularly works in Gaza was attacked by ultra-right militants, leaving at least three people with minor injuries, according to police and witnesses Saturday evening.
The author Christophe Oberline told AFP the group, armed with batons, tried to storm the gathering, attempting to break down the door to the hall although failed to get in.
Organiser Jerome Faynel said the attack was by the "extreme right", and added they were also armed with iron bars and glass bottles.
At least one person was arrested, the police prefecture said, adding they "strongly condemned the violence committed."