The man, who has not been named, was a passenger in a black Ford Fiesta which struck the cliff at the bottom of Mont de la Pulente at about 3.46 am on Sunday.
According to the States police, who attended the scene with paramedics and firefighters, the 18-year-old male driver and two 19-year-old male passengers suffered minor injuries and did not need hospital treatment.
The road was closed for several hours after the crash, which happened as the car travelled up the hill. No other vehicle was involved and no one has been arrested.
Anyone with information – particularly those with dash-camera footage of the vehicle during the evening – is being asked to phone the States police.
In a separate accident at about 8.04 pm on Saturday, an 18-year-old woman was taken to hospital with minor injuries after being involved in another single-vehicle collision in Grande Route de St Laurent, near Bon Air Stables.
The woman, who was a passenger in a white Hyundai being driven by a 19-year-old man, spent around two hours in the emergency department before being discharged.