President Francois Hollande of France signed same-sex marriage into law on Saturday after the Constitutional Council dismissed a legal challenge to stop it.
The legislation also legalizes adoption by same-sex partners.
"I will ensure that the law applies across the whole territory, in full, and I will not accept any disruption to these marriages," Mr Hollande said.
Justice minister Christiane Taubira, who brought the bill before parliament, said the first same-sex marriages could take place as early as June.
Deutsche Welle reports the debate has divided France. Opponents of the law are planning a major protest in Paris on 26 May.