It was built during the Great Depression as part of a massive statewide public works initiative to stimulate the economy and provide jobs. Louis Simon, supervising architect for the Treasury Department, used a stripped-down Classical Revival style for the post office, which replaced a much-beloved older one. Painter Waldo Peirce added two murals to the building's lobby in 1938, making Troy's one of only three post offices in the U.S. with his artwork.
The post office is a two-story, 7-by-10-bay steel frame building on granite foundation. Its two main facades (Broadway and Fourth) frame their entrances with engaged two-story pilasters on molded bases and capitals. At the top of the pilasters is a simple frieze. At the end bays the frieze is decorated with abstract stars and stripes with winged shields at the corners, where the stone surface beneath them changes from ashlar to rusticated. The Broadway frieze has the words "UNITED STATES POST OFFICE", reflecting the main entrance located underneath it.
That main entrance is reached by a set of granite steps. It is surrounded by limestone and flanked by original wrought iron lamps and lampposts. The windows to the sides are trimmed in decorative limestone as well, their bays recessed like the main entrance and the central eight bays of the Fourth Street side. A secondary entrance, similar to the main entrance but with less decoration, is located two bays north of Broadway.
The north and east (William Street) facades are faced in buff-colored brick laid in common bond, with limestone coping. To the north the building projects one bay from the main section; this ell includes the loading dock facilities. A brick chimney rises from the northeastern corner.
Inside, two connected lobbies parallel the main facades. An original glazed aluminum vestibule on the main entrance, and a small marble lobby on the secondary, give way to a terrazzo floor, dark green marble base and veined white marble dado. The plaster walls are divided into four recessed bays flanked by marble pilasters, rising to a ceiling cornice with classical detailing. While the furniture in the lobbies is newer, most of the teller windows and the iron grillework above them, and some of the post office boxes, are original.