Mellon supported the construction of a building that would represent the rise of Pittsburgh and western Pennsylvania to national political and economic prominence.

[3] The New York architectural firm of Trowbridge & Livingston designed the building under the auspices of Supervising Architect of the Treasury James A. Wetmore.

[3] During the 20th century, the building underwent several significant interior alterations, which included the addition of new courtrooms and the removal of the train tracks.

Ten years later, the building was individually listed in the National Register of Historic Places as the US Post Office and Courthouse-Pittsburgh.

[5] The Grant Street Station Post Office, which had been in the Seventh Avenue section of the building since its opening, closed permanently at 2:00 p.m. EST on Saturday Afternoon, February 15, 2014.

The U.S. Post Office and Courthouse occupies the entire block bounded by Seventh and Grant streets and the Pennsylvania Railroad.

The second mass is set back slightly and includes the fifth through eleventh floors, which contain courtrooms, jury rooms, judge's chambers, and other offices.

[3] The Post Office and Courthouse has a steel frame clad in granite on the lower levels, while the upper stories are faced in limestone.

The lower portion of the building is covered in rusticated blocks that provide an appropriate foundation for the tall arched window and door openings that dominate each elevation.

The first floor contains an elaborate groin vaulted, terra cotta ceiling with gold-leaf trim, now visible from the main lobby.

Three murals were commissioned for the courtrooms under the Treasury Section of Painting and Sculpture and installed in 1936 and 1937: Steel Industry by Howard Cook; Pittsburgh Panorama by Stuyvesant Van Veen; and Modern Justice by Kindred McLeary.

The General Services Administration commissioned Brian Shure and Lia Cook to create new works of art.

Cook's work, a textile painting depicting images of children, combines hand weaving techniques with computer technology.