Police said the man, in his 50s, was walking on the A48 near the Northgate House bed and breakfast in Caerwent when he was struck at about 03:30 GMT.
The man, who is from Caerwent, was taken to Newport's Royal Gwent Hospital, but died shortly after arrival.
Anyone who witnessed the crash is asked to call Gwent Police on 101.
A man has died after being hit by a car in Monmouthshire.