His signature means the first gay marriages may be celebrated in France within about 10 days. Hollande's office said he signed the bill Saturday morning, a day after the Constitutional Council struck down a challenge to the law.
Hollande, a Socialist, had made legalizing gay marriage one of his campaign pledges last year. While polls for years have shown majority support for gay marriage in France, adoption by same-sex couples is more controversial. The bill prompted months of widespread protests, largely by conservative and religious groups. Some were marred by clashes with police. It became a flashpoint for frustrations at the increasingly unpopular Hollande.