Graduate of the Evelpidon School. He joined the Engineer and participated in the unfortunate Greek-Turkish war of 1897, as a captain. He was a high-ranking member of the National Society. He was later entrusted with the direction and inspection of the Engineer. In the Balkan wars he served as a colonel and commander of an independent detachment of Euzones. He maneuvered to capture Sarantaporo and then the Turkish troops under his pressure left Grevena, to triumphantly enter the city with his Euzones.

On 26 October 1912 he was promoted to Major General and became Commander of the 5th Division. After the victorious battles in Kilkis, Komano Kozani and Tzoumagia , Gennadi remained with the 5th Division as commander of Drama and then as commander of the 4th Army Corps in Kavala. In 1916 Rupel and Kavala was captured by the Germans and their Bulgarian allies. Gennadis, who was then on leave in Athens because of his support for the King, was demobilized and exiled to Santorini.

In 1920, with the return of King Constantine, he was recalled to active service and given the command of the Gendarmerie. He then became Commander of the Higher Military Administration of Old Greece, ASDPE (1921).