Smelling blood after a bruising first year for President Francois Hollande, right-wing leaders have mobilised a fierce campaign.
But sociologists argue that France's social fabric and identity crisis also helps explain the ferocity of the debate.
The cheers and Maori love song that greeted the legalisation of same-sex union in New Zealand's parliament Thursday were in stark contrast to the escalating rage a similar bill is causing in France.
In parliament, MPs nearly came to blows this week; gay activists have reported a rise in attacks on homosexuals; and millions of people have taken to the streets to declare their opposition to the bill, vowing to fight to the bitter end.
The divisions over gay marriage in France follow political lines, and the opposition has united against the bill, seizing an opportunity to pile pressure on an already embattled administration.
"It was the first chance for the right-wing electorate to express their opposition to Francois Hollande's presidency and (Prime Minister) Jean-Marc Ayrault's government," political analyst Jean-Yves Camus said.
After Nicolas Sarkozy's failed reelection bid and subsequent political retirement left France's mainstream right in tatters, the opportunity was threefold for his UMP party, Camus said.
"It is now an opposition party and needs fresh momentum. The negative social and economic context favours the spread of discontent, and the president's ratings are abysmal," he said.
The new law is expected to pass on Tuesday, which would make France the world's 14th country to legalise same-sex unions.
With two days to go, the war of words is still raging between politicians, and riot police are bracing for rival marches on Sunday, with opponents of the bill promising another monster demonstration.
Robert Rochefort, a sociologist and centrist member of the European Parliament, stressed that the furore offered the latest evidence that French society was insecure.
"I think gay marriage is the course of history and will come about in all Western nations but (French) society is cornered by its own fears," he said.
The issue of national identity was a centrepiece of Sarkozy's tenure and of his failed reelection campaign and many in France's ever-growing far-right electorate hope to rekindle the debate.
While the state is fiercely secular, the gay marriage bill showed that a significant section of French society remains staunchly Catholic and conservative.
During the string of demonstrations opposing the bill, some of which drew hundreds of thousands of protesters, families marched alongside royalists, fundamentalist Catholics and far-right nationalists.
Opinion polls have routinely indicated that while a majority of French people support gay marriage, a slight majority opposes adoption rights for homosexual couples.
"It was clumsy of the government to initially suggest that the bill would also legalise medically assisted procreation" for homosexual couples, said Michel Wievorka, one of France's most renowned sociologists.
Jean-Yves Camus argued that the fervour the issue has stirred up in France was "the legacy of a past that still excites passions more than two centuries after the dawn of the republic."
The separation between church and state was a blood-drenched affair in France -- and two centuries on, the divisions still remain, Camus argued.
Catholic fundamentalists may be a small minority, but they are deeply rooted one. And there are still those on the right who will never accept the legitimacy of a left-wing government.
Wievorka however predicted that the bill's supporters would prevail as the other camp was coming apart at the seams, with protests generally losing steam or being hijacked by radical fringe groups.