The two pedestrians, both from Whitby, were struck Thursday night on Dundas Street just east of Hickory Street at about 10:45 p.m., said police communications co-ordinator Jodi MacLean.
The two men were struck while attempting to cross from the south to the north side of Dundas Street, police said.
The vehicle suffered heavy windshield damage, the CBC's Tony Smyth reported.
The driver, who was the lone occupant of the car, was uninjured, MacLean said.
The men were rushed to hospital where the 18-year-old was pronounced dead, MacLean said. The 19-year-old remains in hospital in critical condition.
The accident was believed to be due to snowy weather conditions, as a major winter storm began to hit southern Ontario last night, said MacLean.
"The driver remained on the scene, was uninjured, [and there was] no alcohol involved," she said Friday. "It was believed to be weather related, because that was the beginning of the storm."
The road was closed for several hours while the Durham Regional Police's collision unit investigated the scene.
The investigation is ongoing, but no charges are expected, MacLean said.
The names of the two victims have not been released.