US 231 enters the state from Florida south of Madrid and exits into Tennessee, running councurrently with US 431 north of Hazel Green.

US 231 passes through the major cities of Dothan, Troy, Montgomery, and Huntsville.

Between Wetumpka and Arab, excluding its overlap with US 280 between Sylacauga and Harpersville as well as portions through major towns, the road is largely rural and two lanes.

Between Arab and the Tennessee state line, the route returns to a four-lane divided highway; the route is upgraded to a limited-access freeway and adjoining frontage roads named Memorial Parkway within the city of Huntsville.

In Alabama, US 231 is paired with unsigned State Route 53 (SR 53) from Huntsville to Dothan.

The route passes through mostly straight terrain between the Tennessee state line and Meridianville, which is home to its junction with Bob Wade Lane, which eventually becomes SR 255.

The route continues south as a freeway until it reaches a specific point when it becomes a four-lane divided highway.

While climbing, the route makes a slight curve from the southwest to the southeast that is easily noticeable on road maps.

The route heads through mountainous terrain to Arab, which is home to its junction with SR 69.

The route climbs up a high hill and descends it, now crossing into St. Clair County.

The route heads through extremely hilly terrain as a two-lane and three-lane road.

It parallels the Coosa River as it reaches Vincent, which is home to its next junction with SR 25.

After a long journey to Sylacauga, the route turns off of US 280 at its junction with SR 21, which is a Diamond Interchange.

South of here, US 82 turns off of US 231 and US 231 continues onward on a four-lane divided highway into Pike County.

In Houston County, the route has no major junctions until it reaches the Ross Clark Circle, which is US 84 and SR 210.

The route turns south onto the Ross Clark Circle and heads to the junction with US 84 Bus.

The route turns to the full east and junctions with US 431 once again, for the first time since Huntsville, Alabama, alongside US 431 Bus.

When US 231 was first assigned along with the rest of the United States Numbered Highway System in 1926, the route ran only as far north as Montgomery.

The original route ran up what is now Whitesburg Drive on the south side of the city, and Meridian Street in the north.

A portion on the north side of Brindlee Mountain, south of Huntsville, was damaged by a landslide in 2020.