The 40-year old is believed to have been killed between Friday night and Saturday morning, French media reported on Sunday.
Omar Omsen as he was mknown, succumbed to injuries sustained during an attack on troops loyal to Syrian President Bashar Al Assad.
His death will come as a blow to Islamic State, who had benefitted from the Franco-Senegalese's strong ability to entice foreigners to Syria to fight against government forces.
Omsen succeeded in drawing in dozens of young French men and women from his hometown Nice, through highly sophisticated propaganda videos.
A former graphics designer and video editor, who was documented in the book "French jihadists," Omsen's "films" were often compared to documentaries, for the quality of their music, and special effects.
In them, he would present himself as an "authentic Muslim," and would urge other "true" Muslims not to sit back and let their fellow brothers be killed in Syria by "non-believers."
According to sociologist Dounia Bouzar, who runs France's only deradicalization centre, Omsen's strategy was so effective, that he could recruit young people from rich families who had no connection with Islam.
The strategy -highly controversial- was successful in marrying the cause of Islam with that of saving innocent civilians in Syria's four-year civil war.
Omsen left France for Syria in 2013, and set up his own group, the “Katiba”, under the Front Al-Nosra, a branch of Al-Qaida in Syria.
From there, he began recruiting dozens of foreign nationals, mostly from Nice where he grew up from the age of 5.
His death was first announced on Twitter by the Romanian researcher Caillet, and then later confirmed by journalist David Thomson, author of the aforementioned "French jihadists."