U.S. Route 431 (US 431) is a spur of U.S. Route 31. It currently travels for approximately 556 miles (895 km) from US 231/Alabama State Route 210 and US 231 Business (US 231 Bus.) and US 431 Bus. in Dothan, Alabama, to Owensboro, Kentucky, at US 60 and Kentucky Route 2831.
U.S. 431 is paired with unsigned State Route 1 throughout almost all of Alabama, with the exception of Dothan, where it is paired with signed State Route 210 around the eastern portion of the bypass named Ross Clark Circle. There is also a business route through downtown Dothan signed as Business US 431 and locally known as Reeves Street which runs into Business US 231. The two routes are signed concurrently through downtown and known locally as N. Oates Street north of Main Street (Business US 84) and S. Oates Street south of Main Street. The southern terminus of US 431 is at the intersection of US 231 and the business spurs on the south side of Ross Clark Circle.

The route takes a rather meandering path through southeast Alabama. It heads in a northeast direction to pass through Phenix City near the Georgia state line, then cuts back to the west to pass through Opelika; the portion between Phenix City and Opelika is concurrent with U.S. Route 280. From Opelika, US 431 swings back and forth between northwest and northeast as it works its way through the southern extent of the Appalachian Mountains, then turning northwest to pass through Talladega National Forest, arriving at a junction with Interstate 20 a few miles east of Oxford. The combined routes travel westward from Exit 191 into Oxford, where US 431 splits off at Exit 188 and heads northward through Oxford and the adjacent city of Anniston; through this section the route is named Veterans Memorial Parkway.

From Anniston, US 431 heads northwards towards Gadsden. In East Gadsden, it combines with U.S. Route 278; the combined route passes westward through Gadsden and Attalla before splitting just northwest of Attalla. This route is named Meighan Boulevard in Gadsden and Fifth Avenue in Attalla until reaching US 11. In downtown Attalla, the route shares a brief wrongway concurrency with US 11. West of Attalla, US 431 again turns to the northwest. At Guntersville, it joins with Alabama State Route 79. Through downtown Guntersville the route is divided into two separate oneway streets; the northbound street is named Blount Avenue, and the southbound street is Gunter Avenue. At the northern edge of Guntersville, the split streets combine and the joint route crosses the Tennessee River via the George S. Houston Bridge, before US 431 splits off and again heads in a northwest direction.

At Huntsville, US 431 passes over Monte Sano Mountain and through Huntsville's medical district before reaching Memorial Parkway; this portion of the route forms a portion of Governors Drive. At the Parkway, the route joins with U.S. Route 231; the combined routes then travel northward to the Tennessee state line.