The state highway runs 8.29 miles (13.34 km) from St. Johns Lane in Ellicott City east to Parkway Drive South in Hanover.

When MD 100 was constructed between Glen Burnie and Ellicott City in the 1990s, the state highway was extended to its present western and eastern termini.

St. Johns Lane continues west to Columbia Road, where the county highway turns north toward US 40.

MD 103 heads east as Montgomery Road, a four-lane undivided highway, through a three-quarter diamond interchange with US 29 (Columbia Pike).

Before leaving Ellicott City, the highway intersects the northern terminus of MD 104 (Waterloo Road) and Ilchester Road, which heads east to the hamlet of Ilchester on the Patapsco River, where the county highway provides access to Patapsco Valley State Park and the ruins of the Baltimore and Ohio Railroad's Patterson Viaduct.

The highway crosses a branch of Deep Run and begins to parallel the eastbound side of MD 100.

[1][2] MD 103 is a part of the National Highway System as an intermodal connector from US 1 east to Douglas Legum Drive at Dorsey.

[9] The portion between the county line and US 1 was constructed around 1936; MD 176 originally met US 1 at an intersection just south of the modern US 1–MD 100 interchange.