Reinstated, he held various ship and senior commands during the interwar period, including serving as Chief of the Hellenic Navy General Staff in 1935–36.

[2] As a young officer he took part in the Goudi pronunciamiento in August 1909, as well as in the abortive revolt of Lt. Konstantinos Typaldos-Alfonsatos in October of the same year.

[2] Promoted to Sub-Lieutenant on 29 March 1910, he fought in the First Balkan War of 1912–13 on board the battleship Psara, participating in the battles of Elli and Lemnos and the liberation of various Aegean islands.

[2] Following the electoral victory of the anti-Venizelist royalist parties, he was recalled to active service on 6 November 1920; his dismissal was revoked and he was quickly promoted to commander on 2 December.

Promoted to rear admiral on 21 February 1934, and on 3 March 1935 he was appointed Chief of the Hellenic Navy General Staff, as well as Director-General in the Ministry of Naval Affairs.

[2] On 10 October, along with the heads of the Army, Lt. General Alexandros Papagos, and the Air Force, Air Vice Marshal Georgios Reppas, he toppled the Second Hellenic Republic, restored the Greek monarchy, and installed Georgios Kondylis as Prime Minister and Regent pending the return of the exiled King George II.

[2] Oikonomou remained in Greece during the Occupation, and served in the Directorate-General of the Navy in the Ministry of National Defence of the collaborationist government in 1941–43.