The short A743 links Lanark with the A70Ayr to Edinburgh route, which, while signposted to Lanark from Edinburgh, actually skirts the town to the east.
The route starts on Lanark High Street at a discrete junction on the A73 in front of the parish church. If it wasn't for the fact that the eastern part of the A73 is one way towards the junction, it would be a TOTSO in both directions, but Wellgate is too narrow to take two-way traffic, indeed the A73 past the church is not much wider but just about copes. The A743 continues east along the High Street as it climbs between the shops and becomes D1 almost immediately, although it is a wide street with generous pavements and parking bays. The central reservation has a series of concrete bollards, linked by chains between the lamp posts to prevent traffic from crossing. The central reservation comes to an end just before the junction with the B7017 in order to give room for turning lanes at the traffic lights. Traffic for the A73 turns right here onto the B7017, Bannatyne Street to rejoin that route, while the A743 continues ahead onto St Leonard Street.
The route quickly leaves the town centre with its busy shops behind and becomes suburban, as it continues to climb. Older houses proliferate, but they were built as ribbon development, with mid twentieth century council estates behind, which have also filled the gaps along the roadside. A small industrial site sits at the crest of the hill, opposite the town's water tower and reservoir, which stand alone in a green space between the houses. Soon after this, the route reaches open country, with fields on both sides. There are only a couple of fields, however, before an industrial estate is passed to the right, and then the road goes over the Lanark branch line. The bridge is an original one, narrow, slightly humped and with a blind kink on the far side, which leads onto a long undulating straight. At the end of the straight is a strange wiggle through trees, which leads into the tiny village of Ravenstruther. Both sides of the road are lined by houses for a short distance before the route ends at a TOTSO on the A70. Continue ahead for Carstairs and (ultimately) Edinburgh.
The route was originally numbered as the B715 in 1922, but later, perhaps as early as 1924, it was the first A7xx route to be given Class I status after the original classification.