"Because of its position on a sloping site, the rusticated base of the Longworth Building varies in height from two to four stories.

Ionic columns supporting a well-proportioned entablature are used for the building's five porticoes, the principal one of which is topped by a pediment.

It presents a somewhat more restrained appearance than the neighboring Cannon Building, which was designed in the more theatrical Beaux Arts style.

The Longworth Building takes its place along with the National Gallery of Art (1941) and the Jefferson Memorial (1943) as one of Washington's best examples of the Neo-classical Revival style".

The principal architects were Frank Upman, Gilbert LaCoste Rodier, Nathan C. Wyeth, and Louis Justemente.