Police told people to remain indoors after a man “dressed in medieval clothes” attacked “multiple victims” with a bladed weapon on Saturday night.
A man in his mid 20s was arrested shortly before 01:00 local time (04:00 GMT), officers said.
But residents are still being told to stay inside as an investigation is under way.
The attack took place around Parliament Hill in the historic Old Quebec neighbourhood. First reports of the incident came through shortly before 22:30 local time.
After his arrest near the Espace 400e business park, the man was taken to hospital.
Reporters at the scene have tweeted photos of a police command post outside Quebec’s Parliament Building.