The state highway runs 11.32 miles (18.22 km) from MD 16/MD 331 at Linchester east to the Delaware state line near Federalsburg, where the highway continues east as Delaware Route 18 (DE 18).

Langrell Road is unsigned MD 817B, which follows the county line west to a dead end at Hunting Creek.

The state highway intersects American Corner Road and passes Magennis Farm Airport in the hamlet of Hynson.

MD 318 continues east through an industrial area along Federalsburg Highway, which crosses the Seaford Line track again at-grade.

The state highway crosses Tanyard Branch before meeting the other end of MD 315 (Liberty Road).

[4][5] The state highway was completed west to U.S. Route 213 (now MD 331)/MD 16 near Preston by 1930.

[13] The Federalsburg Bypass bridge over Marshyhope Creek, which was originally built in 1962, was rehabilitated in 2012.