Psarros first saw action in the Balkan Wars as a volunteer, while still being a cadet in the Army Academy. In 1916 he joined the Venizelist National Defence government. He fought in the Macedonian front of World War I, the Allied intervention in the Russian Civil War (in Crimea) as a Captain, where he was injured, and in the Greco-Turkish War (1919-1922) where, thanks to his bravery, his men were able to pass into Greece from Asia Minor without many casualties. Before the war with the Turks, he was sent to France for superior war studies and after his return of Asia Minor he served in the staff of the Army of Evros, which played a critical role to Greek strategy and politics during these years. Subsequently, he taught in the newly created Greek War Academy. Later, he was among the organizers of the new Ministry of Aviation and served as Chief of Staff of an Army division.