Officials said the crash happened at the intersection of Longfields Drive and Chapman Mills Way in Barrhaven at around 10:35 p.m. ET.
The driver of the car lost control and hit a light standard, officials said, trapping three teenagers inside the vehicle. Firefighters removed the roof of the car in order to extract the teens.
Ottawa paramedics said they treated the front passenger, the 18-year-old, who was initially knocked unconscious and taken to hospital in critical condition with multi-system trauma.
A second teen suffered a head injury, but was walking around outside the car by the time paramedics arrived. He was taken to hospital in stable condition.
The third teen suffered upper body injuries and was also taken to hospital in stable condition.
Area roads were closed overnight but reopened at about 4:45 a.m. Sunday.
Police continue to investigate.