The law came into force over a week ago, but organizers decided to go ahead with the long-planned demonstration to show their continued opposition as well as their frustration with President Francois Hollande, who had made legalizing gay marriage one of his keynote campaign pledges in last year's election.
Marchers set off from three separate points across Paris, and by early evening they filled the Invalides esplanade just across the Seine River from the Champs Elysees.
As night fell, several hundred protesters clashed with police, throwing bottles and chasing journalists.
Interior Minister Manuel Valls said police had arrested around 100 far-right protesters who refused to leave following the end of the demonstration.
Meanwhile, in southern France, the 66th Cannes Film Festival gave the Palm d'Or, its top honor, to "Blue is the Warmest Color: The Life of Adele," a French film about a tender, sensual lesbian romance.
Police estimated around 150,000 people took part in the demonstration in Paris, but march organizers claimed on their Twitter account that more than a million people did.
A similar protest in March drew about 300,000.
Around 5,000 police were on duty Sunday because previous anti-gay marriage protests also had seen clashes between far-right protesters and the police.
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