SR 149 begins in Houston County in Erin at an intersection with SR 49 near that route’s junction with SR 13 just outside of Erin. SR 149 then goes northward and crosses into Stewart County.
It continues north and becomes concurrent with SR 46 before entering Cumberland City. In Cumberland City, SR 46 breaks of and goes through downtown, while SR 149 bypass the town to the east. It then intersects the short SR 434, a connector to SR 233 and provides access to the Cumberland Fossil Plant. SR 149 turns to the northeast to parallel the Cumberland River and enter Montgomery County.
It then goes east through Palmyra before ending at intersection with SR 13 and SR 48 just south of Clarksville.