The final approval of the "Marriage for All" bill took place after months of often acrimonious debate and street protests that sometimes turned violent.
France's Constitutional Council gave the bill clearance Friday after opponents challenged the legality of changing the definition of marriage, Radio France Internationale reported.
"I have taken [the decision]; now it is time to respect the law of the Republic," Hollande said.
Hollande and his Socialist Party had made legalizing same-sex marriage their flagship cause since he was elected a year ago, the BBC reported.
The first same-sex wedding could take place as soon as 10 days after the bill's signing, the BBC said Saturday.