Gonatas served his country during the Macedonian Struggle, the Balkan Wars, World War I, the Ukraine Expedition and the Greco-Turkish War (1919 - 1922) as a colonel. After the Asia Minor Disaster, he initiated, along with Nikolaos Plastiras, the revolt that overthrew the Laiko Komma government and King Constantine I.
On November 14, 1922 (OS), Gonatas took over as Prime Minister of Greece. He held that post until January 11, 1924 (OS), when he stepped aside for Eleftherios Venizelos. For his trouble, he was promoted to Lieutenant General in May 1924. After resigning from the Greek Army, Gonatas entered politics and was elected Senator. He served three terms as President of the Senate until that body was dissolved in 1935.