The road starts where the B4518TOTSOs on the northern side of the bridge over the River Severn in the suburbs of Llanidloes. It heads north out of town along Eastgate Street, initially along the valley but then bears left to climb out steeply. After going over two ridges there's a steep descent into the next valley, that of the Afon Cerist. We cross this small stream then go through the hamlet of Cerist before following the valley downstream.
We soon cross the Afon Trannon and enter Trefeglwys, where we run through the village centre and then very briefly follow the course of a Roman road as we reenter open country. Our road detours north to avoid the hill the Roman road goes over the top of. We follow another valley, that of the Colwyn Brook, then climb ourselves over a hill before descending to cross the Afon Carno. All the watercourses mentioned so far flow into the River Severn close to this bridge and so the land here is fairly flat.
The B4569 now enters Caersws along Trefeglwys Road. We cross the Shrewsbury to Machynlleth railway line at a level crossing by Caersws station and then reach a T-junction on the A470. There's a multiplex one block to the right and the B4569 regains its number by turning left along Main Street. Traffic heading in the other direction does not need to multiplex as it can go straight across the A470 and then follow the one-way Station Road. We continue on and leave town, after which there is a glimpse of the Severn to the right. Our road then bends left and ends shortly afterwards on the B4568.