Video footage shows protestors using ropes to pull the statue, which had been in place for 120 years. Demonstrators, who claimed to be supporting the ‘Black Lives Matter’ movement, claimed the statue was a celebration of colonialism and racism.
As the statue fell from its plinth the head, which was bashed against the stone base, was knocked off.
Protestors later took photographs of themselves posing with the decapitated head.
As the statue started falling there was loud cheering and celebratory whooping from the crowd.
Montreal Mayor Valérie Plante condemned “the acts of vandalism that took place this afternoon in downtown Montreal”.
She added monuments are currently at “the heart of emotional debates” about Canada’s identity and colonial past.
Police are currently investigating the incident.
When contacted by CBC Montreal a march organiser declined to comment on the attack.
Ms Plante added: “I understand and share the motivation of citizens who want to live in a more just and inclusive society.
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He died in office during his second term in 1891.
Sir John became Prime Minister after the 1867 British North America Act devolved substantial powers from London to Canada, then a British colony.
A number of statues around the world have been toppled by groups claiming to support the Black Lives Matter movement after George Floyd was killed whilst being arrested by police in May.
In Bristol, UK, a statue of merchant and slave trader Edward Colston was torn down in June and dumped in the city’s harbour.
It was later recovered and put in safe storage by Bristol City Council.
In the United States a number of monuments to former Confederate generals and soldiers have been pulled down during protests.
More mainstream figures have also been targeted including statues of George Washington in Portland and abolitionist Frederick Douglass in Rochester, New York.
Earlier this week two men were shot dead by an armed vigilante in Kenosha, Wisconsin.
It followed protests and riots over the police shooting of a black man which left him seriously injured in hospital.
Police arrested a 17-year-old male, Kyle Rittenhouse, on suspicion of murder.