Born in Ithaca he was a career soldier. He first saw action in 1897 fighting the Turks in the Thessalian campaign. After studies in Germany he returned to join the General Staff and was par tof the modernizing process of the Greek Army before the Balkan Wars (1912-1913). He was made Chief of the General Staff in 1913 and was promoted to General.
A staunch monarchist he supported Constantine I and opposed Greek entry into WW I. Eleftherios Venizelos, the prime minister, resigned over the refusal to aid the Dardanelles campaign and used the war as the major issue in the elections. When he won the March 1915 elections he mobilized the army but was dismissed by the king. In June 1917, with Allied support and 60,000 Cretean soldiers, the king was deposed and Venizelos empowered, declaring war on June 29, 1917.
After a disputed plebisite George II, son of Constantine I, returned to take the throne in 1935. The elections of 1936 produced a deadlock between Panagis Tsaldaris and Themistoklis Sophoulis. The political situation was further polarized by the gains made by the Kommunistikon Komma Ellados (KKE). Disliking the Communist and fearing a coup George II appointed Metaxas, then minister of war, the interim prime minister.
Widespread industrial unrest in May allowed Metaxas to declare a state of emergency. He suspended the parliament indefinitely and also annulled various articles of the constitution. By August 1936 Metaxas was effective dictator. Patterning his regime on other authoritarian European governments he banned political parties, arrested his opponents (around 15,000 Greeks were imprisoned or exiled for political offences by the Metaxas regime), criminalized strikes and introduced widespread censorship of the media. But he did not have great popular support or a strong ideology.
The Metaxas government sought to pacify the working classes by raising wages, regulating hours and working to improve working conditions. For rural areas agricultural prices were raised and farm debts were taken on by the government. Despite these efforts the Greek people generally moved towards the political left, but without actively opposing Metaxas.
In foreign policy Metaxas was caught in a dilemma. He saw Germany and Italy as 'natural' allies but in the Mediterranean the British and their fleet were a major force while the grandiose schemes of Mussolini were clearly threatening to Greece. The uncertain line between the opposing forces was decisively broken by the blunt demands of Mussolini in October 1940. He demanded occupation rights to strategic Greek sites and was met with a single-word reply "no". Italy invaded from Albania on October 28.
The battle for Greece was another failure by the Italians, the Greeks resisted, stubbornly forcing the Italians back and even occupying parts of Albania. Metaxas died in Athens on January 29 and was succeeded by Alexandros Korizis.