It runs parallel to, and about 3 miles (4.8 km) to the north of, the A4, the principal route between Bristol and Bath on the south side of the River Avon.

The A431 begins at a junction with the A420 road to Chippenham at St George, about 1 mile (1.6 km) east of central Bristol.

The Bristol Trust attempted to turnpike the western half of the upper road, but faced opposition from colliers at Kingswood, and it was not fully completed until the 1740s.

In 1935, the Ministry of Transport rerouted the A4 along this route towards Bristol and Avonmouth, curtailing the A431 to its current eastern point at Newbridge.

[8][9][10] Local entrepreneur Mike Watts created a private toll road over agricultural land to bypass the closed section, which opened in August 2014.