SR 20 begins in Dyer County in Dyersburg as the unsigned companion route of US 412 at an expansive parclo interchange with US 51/US 412/SR 3/SR 211.

It then has a parclo interchange with the eastern end of SR 88 before leaving Bells and continuing southeast through farmland to cross into Madison County.

They then continue through more neighborhoods and pass through an industrial area before coming to an intersection with US 70/SR 1, where they make a left to become concurrent with that highway.

ends and SR 20 splits from US 70/SR 1 as it becomes concurrent with US 412 again as the pair exit Jackson as a two-lane highway and continue east.

US 412/SR 20 continue east through farmland to the community of Springbrook, where it widens to a four-lane divided highway and has an intersection with SR 152 just before entering Henderson County.

US 412/SR 20 continue east through countryside and farmland and pass through Crucifer before narrowing to a 4-lane undivided shortly before entering Lexington.

US 412/SR 20 continue through largely wooded countryside before coming to Perryville and becoming concurrent with SR 100, just before crossing a bridge over the Tennessee River and entering Perry County.

The highway has an intersection SR 438 just south of Mousetail Landing State Park before passing through some hills before entering Linden.

The highway then leaves Linden after crossing a bridge over the Buffalo River and continues east to the community of Chestnut Grove, where SR 100 splits off at a Y-Intersection and goes northeast.