[2] He fought in the Greco-Turkish War of 1897, and after promotion to Lieutenant was appointed to teach architecture at the Army academy from 1902 to 1907.

[3] Leonardopoulos was then appointed as chief of staff of the 8th Infantry Division in 1915–1916, before joining the Provisional Government of National Defence of Eleftherios Venizelos in September 1916.

There he was appointed chief of staff of the National Defence army corps and then head of the personnel office in the Provisional Government's Ministry of Military Affairs.

[3] Subsequently, he was named commander of the newly formed Independent Division, which he led as a reserve formation during the Battle of Sakarya in 1921.

[3] In October 1923, however, he changed stance and along with Panagiotis Gargalidis, he led an abortive coup attempt with pro-royalist officers.