After a coup deposed King Constantine during the First World War, Crown Prince George, by then a Major, followed his father into exile in 1917 (see National Schism); his brother Alexander was installed as a puppet ruler by prime minster Eleftherios Venizelos.
When Alexander I died following an infection from a monkey bite in 1920, Venezelos was voted out of office, and a plebiscite restored Constantine to the throne. Crown Prince George served as a colonel, and later a major general in the war against Turkey. During this time he married, on 27 February 1921 in Bucharest, Princess Elisabeth of Romania, daughter of King Ferdinand I of Romania and Princess Marie of Edinburgh. When the Turks defeated Greece at the Battle of Smyrna, the military forced the abdication of Constantine, and George succeeded to the Greek throne on September 27 1922.
Following a failed royalist coup (by Ioannis Metaxas) in October 1923, the Revolutionary Committee "asked" him to depart Greece while the National Assembly considered the question of the future form of government. He complied and, although he refused to abdicate, he left on December 19, 1923 for exile in his wife's home nation of Romania. When a republic was proclaimed on March 25 1924, he was officially deposed, stripped of his Greek nationality and his property confiscated.
His wife stayed in Bucharest whilst he spent more and more time abroad visiting Britain, and his mother in Florence. In 1932 he left Romania permanently and moved to Britain. Elisabeth and he had no children, and were divorced on July 6 1935.
George, who had been living at Brown's Hotel in London, returned to Greek soil on November 25. Almost immediately he and Kondylis disagreed over the terms of a general amnesty the King wanted to declare, and George appointed an interim Prime Minister, Professor Konstantinos Demertzis. New elections were held in January, which resulted in a hung parliament with the Communists (who were anti-monarchist) holding the balance of power. A series of unexpected deaths amongst the better-known politicians (including Kondylis and Demertzis) as well as the uncertain political situation, led to the rise to power of Ioannis Metaxas. On August 4, 1936, George endorsed Metaxas's establishment of dictatorship - the "4th of August Regime", signing decrees that dissolved the parliament, banned political parties, abolished the constitution, and created a "Third Hellenic Civilization. The King, ruling with Prime Minister Metaxas, oversaw a fascist regime in which political opponents were arrested and strict censorship was imposed. An Index of banned books during that period included the works of Plato, Thucydides and Xenophon.
On April 23 the King and the government left the Greek mainland for Crete but after the German airborne attack on the island he was evacuated to Egypt. Once again he went into exile to Great Britain, seemingly at the behest of King Farouk of Egypt and Farouk's pro-Italian ministers.
During the war he remained the internationally recognized head of state, backed by the exiled government and Greek forces serving in the Middle East. In occupied Greece, however, the leftist partisans of the National Liberation Front (EAM) and National Popular Liberation Army (ELAS), now unfettered by Metaxas' oppression, had become the largest Greek Resistance movement, enjoying considerable popular support. As liberation drew nearer, however, the prospect of the King's return caused dissensions both inside Greece and among the Greeks abroad. Although the King effectively renounced the Metaxas regime in a radio broadcast, a large section of the people and many politicians rejected his return on account of his support of the dictatorship. In November 1943 George wrote to the Prime Minister-in-exile Emmanouil Tsouderos, "I shall examine anew the question of the date of my return to Greece in agreement with the Government". Either deliberately or accidentally, the version released for publication omitted the words "of the date", creating the impression that George had agreed to a further plebiscite on the monarchy, even though a retraction was issued.
After two changes of Prime Minister, the establishment of a rival Communist-led government in occupied Greece and a pro-EAM mutiny among the armed forces in the Middle East, it was agreed in the May 1944 Lebanon conference that the fate of the monarchy would be decided in a national referendum. Bowing to Allied pressure, George was forced to appoint Archbishop Damaskinos of Athens as Regent in January 1945. Damaskinos immediately appointed a republican-dominated government. Being ill, exhausted and powerless, George bought a lease on a house in Chester Square, Belgravia and made a home there with his long-time mistress.
On 26 September George returned to Greece to find the Royal Palace looted, the woods at Tatoi chopped down for fuel and corpses buried in shallow graves outside. His country faced economic collapse and political instability.
On 31 March 1947 he was discovered unconscious in his room at the Royal Palace in Athens, and died the following day of arteriosclerosis. When the news was announced some thought it to be an April Fool's joke.
His funeral was held at the Orthodox Cathedral of the Annunciation in Athens.
He was succeeded by his brother, Paul. On account of his many exiles, he is said to have remarked that "the most important tool for a King of Greece is a suitcase.
In Greece he was honored by having a stamp made after him.