The road starts at a gyratory on the A26 in Ballymena town centre and heads southwest along Bridge Street to a fork. The road ahead, Waveney Road, is sometimes marked as a one-way spur of the A523 running alongside the railway line to traffic lights on the A42 Galgorm Road. However, the mainline of the A523 forks left to cross the River Braid.
On the far side of the river the A523 crosses a mini-roundabout to reach a gyratory. The road then continues south along the residential Queen Street to meet the B18 at a mini-roundabout. We continue through the suburb of Ballee and the road is still largely urban by the time we reach the end of the road, a roundabout where we rejoin the A26.