Montreal police say the woman was walking along a downtown street just after midnight when she was set upon.
Police say they have arrested a 38-year-old man, and that he is expected to appear in court tomorrow to face criminal charges.
They say the man had just been kicked out of a bar for aggressive behaviour.
Witnesses say the assailant struck blows to the woman's upper body and then went after her head after she had fallen down.
He backed off after a passerby intervened.
The woman died in hospital a few hours after the attack.