A gunman shot dead one person during a rally by the leader of Quebec's separatist Parti Quebecois in Montreal.
Pauline Marois, the first female leader of Quebec, had just told her supporters the province would one day be independent when her bodyguards rushed her from the stage.
She later returned to finish her speech.
A police spokesman said a man entered the back of the Metropolis theatre and shot two people, before setting fire to the back of the building. One of the victims later died.
The shooting eclipsed the news that the Parti Quebecois had only just defeated the ruling Liberals and would have to be content with a minority government.
The result effectively rules out another referendum on breaking away from Canada.
RDI television showed pictures of police subduing a man with a rifle who was dressed in a black cape.
He appeared to shout in French the phrase: "The English are waking up."
Ms Marois had promised to strengthen laws designed to ensure the dominance of the French language, which has worried some in the minority English-speaking community.
