France's Constitutional Court upheld the nation's same-sex marriage ban Jan. 28.
It said gay and straight couples find themselves in a "different situation" that justifies differing treatment under family law.
Parliament, however, can legalize same-sex marriage if it wants to, the court said.
Polls suggest that nearly 60 percent of French people support letting same-sex couples marry.
The nation has offered civil unions for gay couples for more than a decade, but the unions lack many legal benefits of marriage.