The world-renowned architect Ludwig Mies van der Rohe served as the chief designer with Schmidt, Garden and Erikson; C. F. Murphy Associates; and A. Epstein and Sons all working on the project.

However, vehicular access for the post office required a street-level loading dock that would have intruded on the openness of the plaza between the two buildings.

The site for the new Federal Center included the block occupied by the Beaux-Arts style U.S. Post Office and Courthouse (1898–1905) designed by Henry Ives Cobb, which replaced an 1879 government building in the same location.

The courthouse contains 1.4 million gross square feet of space and is set at a right angle to the Federal Building high-rise across Dearborn Street.

The simple but elegant book-matched black-walnut paneling and molded-plywood spectator benches are lit by ceiling fixtures covered with an aluminum grid.

During the 1990s, additional courtrooms were created within the building in a style complementing the original details; Mies's initial design planned for future expansion of this nature.

The simple and well-proportioned steel-and-glass design of the Chicago Federal Center epitomizes the minimalist architectural approach favored by architect Ludwig Mies van der Rohe.

The exterior curtain walls are defined by projecting steel I-beam mullions covered with flat black graphite paint, characteristic of Mies's designs.

The balance of the curtain walls are of bronze-tinted glass panes, framed in shiny aluminum, and separated by steel spandrels, also covered with flat black graphite paint.

In the early 1970s, the U.S. General Services Administration, under its Art in Architecture program, commissioned a steel sculpture for the plaza from the celebrated artist Alexander Calder.