Marois, who had just become the first female premier of Quebec, was giving her victory speech when a man entered Montreal’s Metropolis concert hall and shot two people, killing one and critically injuring another.
Montreal police confirmed that a man in his 40s was pronounced dead at the scene, while a second man in his 30s was in a critical condition.
Commander Ian Lafrenière of the Montreal police told reporters at the scene: “I would be lying to you to confirm 100 per cent that there was no danger to [Marois] or the people inside, but the shot was fired at the back of the building.”
The shooter, thought to be in his 50s, is reported to have also started a fire on the premises.
A man was arrested outside the venue and a weapon seized, according to CBC News Canada.
The man reportedly entered the venue from the back as Marois was calling for unity among Quebecers. The back door was about six metres from the stage on which Marois was giving the speech, CBC reported.
Marois returned to the stage a short time after the shooting and asked the crowd to leave the venue calmly.
Marois had just become premier-elect after voters ousted the governing Liberals in favour of the separatist Parti Quebecois, of which Marois is leader.
A motive for the shooting is yet to be established.