France's National Assembly on Tuesday was set to vote a key piece of legislation allowing homosexual couples to marry and adopt children, a key election pledge of President Francois Hollande.
The formal vote comes 10 days after lawmakers voted 249-97 in favour of its key article which redefines marriage as a contract between two people rather than between a man and a woman.
That was followed by intense debate in the house. Once passed, it will come up before the Senate next month for approval.
In a surprise development, several members of the right-wing UMP party of former president Nicolas Sarkozy said they could abstain, a move which would facilitate its adoption.
But 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.
After months of frenzied debate, the ease with which the law cleared its first major hurdle has been welcomed by gay rights activists.
"Things are going well and quickly, which is a relief for us," Nicolas Gougain of the Inter-LGBT lobby group had said.
"We've never seen so many deputies arguing the case for equality and for the recognition of different kinds of families. We can now look forward to the remainder of the debate calmly. It's fabulous!"
But it has proved to be a very divisive issue in this officially secular but overwhelmingly Catholic country with hundreds of thousands staging protest marches.
The anti-gay lobby is set to stage a new march on March 24.
Opinion polls suggest a clear majority of French voters support the right of gay couples to wed and a narrower majority favour them being granted the right to adopt as couples. Gay men and women can already adopt as individuals if approved by social services.
Massive demonstrations across the country, many of which were mobilised by the Roman Catholic Church, have underlined that those who oppose gay marriage feel strongly about the issue.
Hollande has been accused of pushing the legislation through without proper consultation.