The footage was captured around 5pm during a Buffalo Circus show in Doullens, northern France on Sunday afternoon.
In the clip, which was posted on Facebook, the lion can be seen launching its attack on its tamer while shocked crowds looked on.
The animal began dragging the victim, who was in his 30s, around the pen as children screamed in horror. One man can be seen hastily carrying his child away to avoid it witnessing the gruesome scenes.
A fire extinguisher was fired at the 6-year-old lion by workers to distract the animal, allowing the keeper precious seconds to free himself.
Parents can be seen swiftly leaving their seats with their children during the attack.
The man is seen stumbling to his feet before rushing out of the pen.
The video shows him gripping his neck with his hands as he left the cage.
According to local media, the man was rushed to hospital with serious injuries.
French news outlets claimed that the man was “deeply wounded” by the lions “claws and fangs”.
A circus representative said that the tamer had been working with his lions for several years.
It is reported that some audience members were also taken ill following the disturbing incident.
Reports also suggest that the staff at the circus have said that they can no longer work with the lion following the attack.