Toronto police and paramedics were called to the area of Bathurst Street and Ellerslie Avenue, just south of Finch Avenue West, around 3:30 p.m. for a knife.
Police say they received reports that a man and a woman got into an argument and the woman was stabbed.
When officers arrived, they found two people without vital signs suffering from life-threatening injuries.
Despite rescue measures, the victims were pronounced dead at the scene.
The homicide unit took over the investigation.
Police say a third person was located a short time later with minor injuries. He was taken into custody before being taken to hospital for treatment.
“We are pleased that the incident has been contained. There is no longer a threat to public safety,” said Acting Insp. Roger Desrochers.
The circumstances under which the incident occurred are unknown. Roads in the area are closed for the investigation.