Officers responded to a single vehicle rollover on Davis Drive, east of Bathurst Street, around 2:45 a.m. Friday.
When police arrived at the scene, they found the vehicle and a group of 20 to 30 horses roaming the road.
One victim was found without vital signs, police said.
Police were unable to confirm whether the collision was a direct result of the horses or whether any of the horses were injured.
The police are trying to wrangle the horses off the road.
It is unclear how the horses ended up in the area.
Davis Drive is expected to be closed between Keele Street and Dufferin Street for some time as police investigate.