The attack happened just before 1 a.m. in an apartment on Maurice Duplessis Boulevard.
Montreal police said a man entered the apartment, though it's not clear yet if the victim let him in or he forced his way in.
The suspect "inflicted several wounds to the victim with an object," said Const. Raphael Bergeron.
A neighbour who tried to help the woman as well as the victim's 13-year-old son were taken to hospital as well to be treated for shock.
Police arrested a man in his 30s at the scene. Investigators have yet to confirm the motive for the attack, but it appears the man and the victim were at one time in a relationship.
The woman remains in serious but stable condition in hospital.