Guillaume Melanie, head of the Urgence Homophobie association which helps people seeking refuge from LGBT violence around the world, said he was attacked as he was leaving a restaurant with a group of activists.
"Tonight it's my turn," Melanie tweeted, alongside a picture of his bruised, blood-streaked face.
Melanie told the AFP news agency that the group was out celebrating after a foreign victim of anti-LGBT violence who sought his association's help obtained a French residence permit.
"We were somewhat obstructing the way in the street and a man pushed us rather violently.
"I said 'Go easy' and then another man who was with him said 'You're just a dirty faggot' and 'You should all be burned' and punched me hard."
Melanie, who received messages of support from across the political spectrum, said he suffered a broken nose and that he would file a police complaint.
The French capital has been the scene of several homophobic attacks in recent months that have made it into the headlines.
Tweeting her support for Melanie the mayor of Paris, Anne Hidalgo called for a "collective jolt" in the face of homophobic violence and invited Melanie to work with the city and other NGOs on an action plan.
"There can be no question of resigning ourselves to this violence," she said.
Earlier this month, a gay couple were insulted and attacked for kissing on the street in the northeast of the city. One of their two attackers was apprehended and sentenced to a year's imprisonment.
And last month, a young actor, Arnaud Gagnoud, was insulted and beaten with a helmet after hugging his partner outside a theatre in eastern Paris. A teenager has been charged over the attack, which left Gagnoud needing seven stitches.