Protesters marched from Paris’ business district, La Défense, to the Arc de Triomphe, attacking Hollande's government of ignoring pressing issues while pushing ahead with his election pledge of "Marriage for All."
Banners held up from balconies read: "We want work not gay marriage," and "No to gayxtremism."
The Paris police had turned down a request from the protest organisers to march on the famous Champs-Elysees on the ground it would be a threat to public order, partly because it borders the French presidential palace.
A bill to legalise gay marriage and adoption rights comfortably passed France’s lower chamber of parliament last month, and will go to the Senate for examination and approval in April.
The upper house is unlikely to block the reform, but the protesters want the government to withdraw the bill and put it to a referendum.
Virginie Tellenne, a Parisian socialite who goes by the name of Frigide Barjot – meaning Frigit Loony – has been the public face of the anti-gay marriage movement.
"We want the president to deal with the economy and leave the family alone," Tellenne said.
A campaign orchestrated by the Catholic Church and belatedly backed by the mainstream centre-right opposition is steadily gathering momentum.
But Hollande's support for the legislation has not wavered and his partner, Valerie Trierweiler, has revealed that the president will be attending the marriages of gay friends once the legislation is on the statute books.
A separate law on providing medically assisted conception to gay couples, already extended to heterosexual couples unable to conceive, will be debated later in the year.