Another man was seriously wounded when the gunman fired a rifle into a crowded concert hall in Montreal as the party’s leader, Pauline Marois, was making her victory speech.
Bodyguards quickly whisked her away to safety while police arrested the alleged gunman, who has been named by local media as 62 year old Richard Henry Bain, a businessman.
It is also alleged the gunman started a fire near the hall.
Caught on camera during the arrest, the suspect shouted in French: “The English are waking up!”, apparently referring to the English-speaking minority in Québec, which is largely Francophone.
The Parti Québécois favours independence from the rest of Canada but is not expected to push for a referendum on the issue immediately.
Shortly before the shooting, Marois reportedly told the crowd: “The future of Québec is to be a sovereign country.”
Local media say the dead man, 48, and the injured man, 27, worked as technicians for a production company.
The shooting marred celebrations for the Parti Québécois and Pauline Marois, who will be the province’s first ever female Premier.
The Parti Québécois defeated the incumbent Liberal Party and the newly-formed Coalition Avenir Québec, but did not win an absolute majority.
Marois, the Canadian Prime Minister, Stephen Harper, and all the major political parties have condemned the shooting.