A 51-year-old man was stabbed to death inside an apartment on Pigeon Avenue.
Police were called to the scene around 8:30 p.m. Tuesday.
They found the younger man on site. He had also been stabbed.
He was arrested and transported to hospital, where he is under police surveillance.
Investigators will speak to the man as soon as his condition permits them to.
Police do know that the victim and the alleged killer knew each other.
This is Montreal's ninth homicide of 2015.