Designed by renowned architect George Browne Post, the building features terra-cotta ornamentation on the facade and an innovative truss system to support the ceiling of the central library. Architectural historians have praised Post’s design for blending technological innovation and graceful aesthetics.

The building’s masonry consists of unglazed terra-cotta and repressed brick. It was the first building in New York City to use locally produced terra-cotta. The facade is adorned with busts of Christopher Columbus, Benjamin Franklin, William Shakespeare, Johannes Gutenberg, Ludwig van Beethoven, and Michelangelo Buonarroti sculpted by Olin Levi Warner. The busts are interspersed with representations of American flora by Truman H. Bartlett.

Post employed artists and craftsmen of the aesthetic movement to embellish the interior spaces. Stained-glass lunettes and a central laylight are believed to have originated from the studio of noted artist Charles Booth. Design elements throughout the building include Minton tile floors, custom-made bronze hardware (designed by Post), and elaborately carved black ash woodwork in the library.

Inspired by the design of the Brooklyn Bridge, Post suspended the top floor of the building from iron trusses in the roof, creating an open and elegant reading room. Additional iron columns enclosed in carved wood support the galleries in the library.

Brooklyn Historical Society is one of the few remaining examples of an institutional model common in the nineteenth century: the combined museum and library. The vestibule, lobby, stairs, and library were all listed in 1982 by the city of New York as interior landmarks — a rare designation in Brooklyn. In 1992, the entire building was added to the National Register of Historic Places.