The bill, intended to make France the 14th country in the world to allow same-sex marriage, is expected to be comfortably carried given the comfortable majority enjoyed by the ruling Socialists and their allies in the lower house National Assembly.
In February, deputies voted 329-229 in favour of the bill on its first reading and a similar result is anticipated when the formal ballot on the second and final reading takes place around 1500 GMT.
Supporters are planning a celebratory rally and opponents will stage protests in Paris and across the country, but that is unlikely to be the end of what has been one of the most divisive debates in France's recent history.
The bill, which will also accord gay and lesbian couples the right to adopt children, will only become law when it is signed by President Francois Hollande and published in the Official Journal.
Opposition parties are hoping to delay that step by challenging the measure through France's constitutional council.
Even if that appeal is quickly dismissed, they will hope that Hollande can be pressured into a decision not to sign the law into force.
That has happened before. Former president Jacques Chirac shelved an unpopular employment law in 2006 in the face of public hostility.
But all the signs are that Hollande will stick to his guns on the issue, despite a popularity slump that has left him with one of the lowest approval ratings any French president has ever endured.
The opposition UMP has succeeded in making the gay marriage issue a focus of broader discontent with the government, which has also come under fire over the parlous state of the economy and the recent resignation of Hollande's budget minister for tax fraud.
The Socialist leader could scarcely have anticipated the scale of the opposition he would face over a reform that initially seemed to enjoy solid majority backing among French voters.
Recent polls have suggested a campaign in which the Roman Catholic Church initially played the leading role has shifted opinion to the extent that the electorate is fairly evenly split on both gay marriage and adoption.
Against that background, the debate has become increasingly acrimonious in recent weeks with the Socialists accusing the UMP of making common cause with the far-right Front National (FN) over the issue.
There have also been reports of a spike in homophobic attacks and claims that far-right extremists have been responsible for some initially peaceful protests degenerating into violence.
source: www.abs-cbnnews.com
