He was named for two prominent abolitionists, Henry Highland Garnet and Frederick Douglass. He was known for his architectural, engineering, and landscaping work, including Oakwood Cemetery and Prospect Park in Troy, and Forest Park Cemetery in Brunswick, New York.
During his work on the extension of a lock on the Oswego Canal, Baltimore developed a system to test cement that was adopted as standard by the State of New York. He was an inductee of the Rensselaer Hall of Fame. Each year Rensselaer hosts the Garnet D. Baltimore Lecture Series in his honor.
In February 2005, Troy mayor Harry Tutunjian ceremonially renamed the section of Eighth Street between Hoosick Street and Congress Street as Garnet Douglass Baltimore Street, "as a lasting tribute to a Trojan who gave so much to his community."