According to the police, 125,000 demonstrators marched to the famous Place de la Bastille, the site of the French Revolution, to put pressure on French lawmakers to grant equal marriage and adoption rights.
The National Assembly is due to discuss the changes from Tuesday. The laws would constitute the greatest social reform since the abolition of the death penalty in 1981.
Already, parliamentarians have received more than five thousand submissions for amendments.
Paris’s openly-gay mayor, Bertrand Delanoë, was one of the people who took part on Sunday’s demonstration.
“These are changes that wouldn’t take anything away from anyone. It would make French society more free, more comfortable,” he said.
A survey published on Saturday the French news website Atlantico found 63 percent of those surveyed supported gay marriage.
But the same survey found 51 percent of people were against giving adoption rights to same-sex couples.
Delanoë said recent protests against same-sex marriage have been “pretty aggressive”, but the survey results showed “more than sixty percent of French people understand that equality in love and adoption is, in the end, progress for everyone.”
A right-wing politician and former French minister under Nicholas Sarkozy, Roselyne Bachelot, also lent her support for same-sex marriage.
“I’ve been fighting for equal rights for heterosexual and homosexual couples for forty years. I remember very well when we were trying to promote civil unions several years ago…there were only four or five of us (politicians),” she said.
“We went to go see right and left-wing politicians who said: ‘What is this? But we got through to them and we won, and we’ve seen more and more people joining our fight. And we will continue,” she added.
Some members of the conservative UMP party – Sarkozy’s party – are calling for a referendum on the issue.
Gay marriage was one of President François Hollande’s key pledges.