Gilbert was born c. 1864 in Hephzibah, GA. His parents were slaves. After study at Paine College, he earned B.A. and M.A. degrees in Greek at Brown University. In 1890 he went to the American School in Athens, Greece, the first black to do so, and helped draw a map of Eretria, (American Journal of Archaeology, 1891). He taught Greek at Paine College until his death.