Police are appealing for witnesses after the incident near Cramond Bridge at about 03:15.
Officers said the man was understood to have been walking on the northbound carriageway when he was struck by a blue Volkswagen Touran.
He was taken by ambulance to the Royal Infirmary of Edinburgh.
A 50-year-old man is in a serious condition in hospital after being hit by a car on the carriageway of the A90 north of Edinburgh in the early hours.