The road starts off bypassing Bathford to the west. It then climbs up the hill known locally as Sally in the Woods, on the edge of the CotswoldsArea of Outstanding Natural Beauty, which has been the scene of a fatal accident.[2]
The road summits at the turn-off to Monkton Farleigh,[3] at an altitude of 144 metres. After this, the road quality improves in that it widens and is straighter. This continues up to the approach to Bradford-on-Avon. Through Bradford-on-Avon itself, the road descends a steep 1 in 7 (14%) hill, known as Masons Lane. This is the road's main bottleneck since this leads to Bradford-on-Avon's only vehicle bridge over the River Avon (which splits the town in two), and at this stage travellers have merged with traffic from Melksham, Corsham and Chippenham (B3109) which is fed here.
The road passes on towards Trowbridge. 1/4 mile (400 m) after Town Bridge, traffic to Frome splits off upon the restart of the B3109 which had been concurrent with the A363 for a short distance, thus easing congestion. The road passes over a low hill, then descends into Trowbridge.
It is concurrent for a short distance with the A361, then emerges as Bradley Road. There are three roundabouts as the road goes through North Bradley via the White Horse Business Park, to the south. Until the 1980s it passed through North Bradley's residential lane, but since the opening of the business park, the older road through North Bradley became declassified. The A363 then terminates at a roundabout with the A350 in Yarnbrook.
When it was first designated in the 1920s, the road continued on from Yarnbrook as far as Chippenham, but by 1948 this stretch had been redesignated as a continuation of the A350.
