The man was hit on the A466 Wye Valley Link Road in Newhouse, Chepstow, at about 17:00 GMT on Tuesday.
The road was closed in both directions between the M48, junction 2 (Newhouse Interchange) and A48 / Fair View (Highbeech roundabout).
Gwent Police said it would remain closed for several hours.
The Welsh Ambulance Service said a rapid response car and an air ambulance from Filton airfield, near Bristol, were sent to the scene but the man was pronounced dead.
A 72-year-old pedestrian has died following a collision involving two cars in Monmouthshire.