A man fired a gun during a midnight victory rally for Quebec's new premier, killing one person and wounding another.
The new premier, Pauline Marois of the separatist Parti Quebecois, was whisked off the stage and uninjured.
It was not clear if the gunman was trying to shoot Ms Marois, whose party favours separation for the French-speaking province from Canada.
Police identified the gunman only as a 50-year-old man. Police said he set a small fire behind the building before he was arrested.
Ms Marois returned to the stage after the shooting and asked the crowd to peacefully disperse.
Police said they do not know the gunman's motive, but say the suspect, while being dragged toward the police cruiser, shouted in French: "The English are waking up!"