The priest then attempts to pull the child closer before a bearded man grapples him away.
The clip shows the baby being held in a woman's arms as she stood beside another woman and man beside a baptismal font in a church.
But when the baby continues to wail, the priest slaps the tot in the face with his left hand.
Newsweek reported that the priest says, in French, that the child is having a "tantrum" and that water must be poured on his head so he could become a "little Christian".
"I don't care if you're a pastor, priest or one of Jesus 12 disciples", one angry viewer tweeted. "If. You". The cry of the baby annoyed the priest so much that he ended up slapping the child.
However, not quite enjoying the ceremony, the baby suddenly began crying out loudly.More news: Melania Trump wears ‘I really don’t care’ jacket to visit DETAINED children
He grows frustrated and slaps the baby in his face.
The priest was heard saying afterwards: "There, you have to calm yourself, you have to calm yourself, there, there". The clergyman then tells the child to: "calm down, calm down, you must calm down".
Another person said: "If that video would end with the father giving the priest a very strong bitch slap it would be ideal".
Many people online have been outraged by the priest's behaviour.