Route 149 begins at an intersection with Route 28 (Falmouth Road) in the town of Barnstable, within the community of Marstons Mills. Passing Mill Pond, Route 149 proceeds northeast through Marstons Mills, as the two-lane Contuit Road. In Marstons Mills, the route junctions with River Road and Main Street, a double fork in the center of the community. Route 149 passes multiple homes, leaving Marstons Mills as it passes Hamblin Pond. After Old Famouth Road, the highway winds north along the east side of the pond, and passes Cape Cod Airport.