Otto Gentil was the son of the manufacturer of pumps and art collector Anton Gentil of Aschaffenburg. From 1926 till 1939 he was a teacher at the Aschaffenburg School of Arts. Otto married Johanna Gretel Niedermeier, daughter of Karl Niedermeier and Johanna Ney, on 8 March 1931 at Landau, Pfalz, Germany. After the Second World War he rebuilt his Studio in his hometown and continued as a private artist of sculpture and painting.
A few of his sculptures have survived destruction in and around Aschaffenburg till today.