The A403 was opened in about 1970 after the Severn Bridge was opened in 1966, to provide a direct route between the then M4 motorway and Avonmouth. It was initially known as the Avonmouth Aust Coast Road. Between the M4 at Aust and Pilning it replaced the B4055 on a realigned route. Between Pilning and Chittening it followed a new route beside the ICI Severnside plant, and from Chittening to Avonmouth it followed the route of an existing unclassified road, St Andrews Road. At Avonmouth it connects with the A4.
Around 8000 vehicles a day use this road, which recently underwent speed restrictions, between Bristol and Severn Beach, to 50 mph.