Route 126 begins at an intersection with Providence's North Main Street, which is signed US 1.

The route forms a skewed intersection with Power Road, afterwards narrowing to two lanes, and continues through a dense residential area as it skirts the west side of Pawtucket.

West of Lincoln Woods State Park and within the Lincoln town limits, Route 126 turns onto River Road, just south of Route 123, which it intersects shortly after.

The route then enters Manville, where it curves westward before turning right at an intersection with Sayles Hill Road, continuing north.

As it enters Woonsocket, the road begins to parallel Blackstone River more closely, the two straddling a railroad alignment.