SR 99 begins as a secondary highway in Wayne County in Waynesboro at an intersection with US 64/SR 15 just east of downtown along a former alignment of US 64.

The highway then passes by several homes and businesses before turning north onto Natural Bridge Road, where it leaves Old Hwy.

SR 99 goes through some rural areas before becoming very curvy as it passes through Ashland and begins paralleling the Buffalo River, shortly before crossing into Lewis County.

They then come to an intersection with Mercury Boulevard, where US 70S/SR 1 split off to the east and SR 2 begins concurrent with US 41/SR 99 (SE Broad Street).

The highway then heads south for a short distance before SR 99 splits off at a Y-Intersection onto Bradyville Pike as a 2-lane road.

SR 99 then passes through several neighborhoods before leaving Murfreesboro and continuing east through farmland and countryside before crossing into Cannon County.