PARIS — Thousands of people marched in Paris on Sunday to show their support for a same-sex marriage bill that lawmakers will begin to debate on Tuesday.

Demonstrators waved banners emblazoned with phrases like “Equality of rights is not a threat” and chanted: “What do you want? Equality! When do you want it? Now!” Another placard showed a version of the French government’s seal, but with two Mariannes kissing. Under the words “Liberty, Equality, Fraternity” was the slogan “No more, no less!”

According to the police, the march attracted about 125,000 people, twice the number that took part in a similar demonstration in mid-December. Two weeks ago, a rally by those opposed to the proposal drew what the police said were 340,000 people into the streets of Paris.

President François Hollande, a Socialist, promised during his campaign to legalize gay marriage within a year of taking office in May 2012. And with effective majorities in both houses of Parliament, Mr. Hollande and his government should be able to defeat various efforts by opponents to kill or amend the bill. It has been suggested that even given the long legislative process, the bill could become law as early as May.