Initial estimates indicate that over 250,000 people gathered at the opening of the rally which is expected to reach much bigger numbers by the end of the afternoon, say rally organizers.
Tens of thousands of participants have also been reported in other French cities, such as Lyon and Montpellier.
Today's protest (27 January) are being held two days before a parliamentary debate on the government’s marriage equality bill, known as ‘mariage pour tous’ (‘marriage for all’) which will allow gay couples the same rights as their straight counterparts.
Protestors travelled by coach, train and car from across the country to demonstrate in support of same-sex marriage and adoption rights for same-sex couples.
According to France24, French Police estimates that at least 125,000 people joined the rally for gay marriage in Paris, France.
As participants poured into the south of the capital many tweeted that they would not be discouraged by the rainy weather.
The rally started at Denfert-Rochereau square and made its way to the direction of the Bastille, Paris, banners included 'Homosexuality is not a choice: Equality is', 'Equality of rights is not a threat' and so on...
The rally was led by a banner saying ‘Equality Now, always against discrimination’ starting shortly after 2 pm.
Among the demonstrators were prominent politicians, including the chair of the Socialist Party , Harlem Désir, and the former Minister of Health, Roselyne Bachelot, of the opposition UMP party.
Defying the UMP’s official stance against marriage equality Bachelot said: The bill will give more rights to same-sex parents’.
She added: ‘I am for medically assisted procreation to be open for women’.
In an interview to the weekly Journal du Dimanche, French justice minister Christiane Taubira reiterated today her belief that the bill will correct ‘a situation of flagrant inequality.
‘The bill simply gives the same rights and duties to same-sex couples: the conditions of marriage will remain unchanged’, she said addressing opponents who allege the ‘nature’ of the family will be challenged.
‘This bill will protect all families. It will protect children’s rights’, she said, adding that hundreds of thousands of children currently live in homo-parental families in France, but lack the same security as their hetero-parental peers.
In an interview with France 24, Nicolas Gougain, spokesperson for the Inter-LGBT association said: ‘We’re not demonstrating in response to our opposition.
'We’ve been demonstrating for 10 years already.
‘But this time we hope to surpass the numbers reached at our last march on December 16 [organisers said 150,000 took part, police put the number at 60,000]’.
Gougain described the opponents of marriage equality as a ‘product of unapologetic homophobia in France … largely driven by fear and doubt, something which the opposition is good at aggravating’.
‘Some of those people believe that giving homosexuals the same rights as heterosexuals will destabilise society.
‘Or that homosexual parents are potentially dangerous for their children’.
Support for marriage and adoption equality has actually risen over the past month, despite the active opposition movement.
A poll carried out by Ifop for news website Atlantico.fr last week showed that the proportion of French people who support gay marriage rose from 60% to 63% between early and late January.