Prominently sited on South Mountain, Packer Hall, Lehigh University's principal building, is an aggressively muscular Victorian Gothic essay. It was much admired. Architectural critic Montgomery Schuyler called it “a vigorous and picturesque performance … well adjusted to its commanding site and well adapted to its communal uses.” Those uses included the president's office, chapel, teaching museum, engineering drawing room, classrooms, laboratories, dormitories, and exercise room. The building rises a full three stories, plus an attic floor lit by gable end windows and dormers, and a basement floor. Its three principal massing elements reflect its various functions. The east end was a large classroom and laboratory block with dormitory space in the attic. A more reserved block to the west contained the museum and engineering drawing room, two-story-high windows indicating the larger interior spaces. On the west end, marked by a dominating tower, was the president's office. Potter specified polychrome brick for the building but Asa Packer insisted on stone from local quarries. The result is raucous: rough gray fieldstone tinged by brown iron deposits, trimmed in brick and quartzite, and vividly colored voussoirs in the arches. The scientific mission of the university is delightfully proclaimed in the sculpted column capitals and bases, which depict fossilized ferns, trilobites, and nautilus shells, as well as local fauna; other capitals bear the names of poets, scientists, and philosophers.

There have been a few alterations. The building's tower was damaged by lightning not long after construction, and was rebuilt in 1883 by Addison Hutton without its grandly elongated mansard roof. Later additions to the rear and west end, of matching stone, are hidden from view behind the massive structure. Otherwise, it is in an exceptional state of preservation.