Police said stinging is not a terrorist attack. "Today's event is an individual action that was committed by one person," the police said on Twitter.
The church tweeted
that Father Claude Grou was "out of danger". The 77-year-old priest was taken to a hospital and recovered from his wounds, said Constable Caroline Chevrefils.
The 26-year-old suspect was arrested by security staff in the church and detained by police, Chevrefils said. She said the suspect is known to the police.
Grou celebrated mass for about 60 people in the church and an audience watching the event live as the suspect walked toward the priest and stabbed him several times with a sharp object, Chevrefils said.
The video showed Grou moving away as the man approached, then fell and stood up after the attack. Parishioners separated the attacker from the priest.
The police were summoned to the church at 8:40.
The suspect, whose name was not released immediately, is expected to appear at 13:30 pm in the Quebec Court Criminal Room via video feed Saturday. If any charges are made, they will be determined by prosecutors, Chevrefils said.
Social media filled with sympathy.
"What a terrible attack on the Saint Joseph Oratory in Montreal today," Prime Minister Justin Trudeau tweeted . "Father Claude Grou, the Canadians are thinking of you and wishing you a speedy recovery."
Montreal Mayor Valerie Plante tweeted
: "What a terrible and inexcusable gesture that has no place in Montreal Life of Father Claude Grou, the rector of @osjmr, is not endangered and his condition is stable. On behalf of all Montrealers I wish him a speedy recovery. "
Christian Lépine, archbishop of Montreal, posted a statement on the Archdiocese's website thanking police, paramedics and parishioners for their response."
"We are all shocked by a violent act that took place here on one Lépine said
St Joseph's Oratory, Canada's largest church, is located in the culturally diverse Côte-des-Neiges district.
CNN's Tony Marco contributed to the event to this report.