The shooting followed preliminary results indicating the party was on course to form a minority government after nine years in opposition.
PQ leader Pauline Marois was giving a victory speech in Montreal when shots were heard at the back of the hall.
She was rushed off the stage and a man was arrested.
The gunman’s target was unclear but the 50-year-old suspect was heard shouting in French “The English are waking up”, as he was led away in handcuffs. TV pictures showed him wearing a balaclava and what looked like a blue dressing gown over black clothing.
Two shots were reportedly fired. One was man was fatally wounded, another is in a critical condition in hospital.
As the suspect was led away, firefighters were called to put out a fire that had been lit outside the building.
The attack marred PQ celebrations after claiming a projected 54 of the 125 seats in the primarily French-speaking province.
It is unclear whether the party’s victory will lead to a new referendum on separation from the rest of Canada.
Previous PQ governments held such votes in 1980 and 1995, but both failed.
The party leader had just expressed her desire for Quebec’s independence when the shooting happened.
Popular support within Quebec for another referendum is low, but Pauline Marois has promised to hold one if the “winning conditions are right”.
She has listed a series of demands for Canadian PM Stephen Harper if her party gains power, including further strengthening of laws to protect Quebec’s French language and identity.
“I would like to have the responsibility about the linguistic policy – about the French policy on the territory of Quebec. About culture, about communication and we would like to have the responsibility of the unemployment programme.”
Pauline Marois, 63, will now become the province’s first female premier.
The PQ was competing against the governing Liberals and a popular new party, Coalition Avenir Quebec (CAQ).
Incumbent Liberal Premier Jean Charest has lost his seat.
His party is on course to lose 14 seats, giving it 50 rather than 64 in the outgoing parliament.
But Jean Chartest stressed that the PQ had only gained a minority victory:
“The result of this election campaign speaks to the fact that the future of Quebec lies within Canada.”
The almost six million people eligible to vote in the only majority French-speaking province of Canada choose 125 members of the national assembly (MNAs).
Many voters contend that the main issue is Quebec’s flailing economy.
The province is weighed down by a staggering C$184 billion ($186 billion) of debt.
Quebec has also been beset for the past year with large student demonstrations – some violent – opposing the government’s attempts to increase tuition fees.
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