Route 149 begins as Main Street at an intersection with Route 82 in town center of East Haddam and heads north along the Connecticut River, then northeast as East Haddam-Moodus Road along the Moodus River.

On entering Colchester, it continues north and northeast, as Westchester Road intersecting with Route 16 in the village of Westchester.

After crossing the Jeremy River, it enters the village of North Westchester, where it has an interchange with Route 2 (at Exit 16) and then terminates 0.1-mile (0.16 km) later at an intersection with Old Hartford Road (an old alignment of Route 2) at the town line with Hebron.

[1] The section of Route 149 from the southern terminus to milepost 2.31 in East Haddam is designated as a scenic road.

[1] This portion of the road runs through the East Haddam Historic District along the banks of the Connecticut River and Moodus River.