Paul was born in Athens, the third son of Constantine I, King of the Hellenes and his wife, Princess Sophia of Prussia. He was trained as a naval officer.

On 9 January 1938, Paul married Frederika of Hanover at Athens. They had three children: Sophia, ex-Queen of Spain (born 1938); Constantine II, ex-King of the Hellenes (born 1940); Irene, ex-Princess of Greece and Princess of Denmark (born 1942).

Before his marriage he is alleged to have invited the homosexual literary muse, Denham Fouts, on a cruise of the Aegean Sea, perhaps because they were lovers. However, Fouts's friend John B.L. Goodwin said Fouts often made up stories about his life, and literary critic Katherine Bucknell thought many of the tales about him were myth.

From 1917 to 1920, Paul lived in exile with his father, Constantine I. From 1923 to 1935, and again from 1941 to 1946, he lived in exile again, this time with his brother, George II. During most of World War II, when Greece was under German occupation, he was with the Greek government - in - exile in London and Cairo. From Cairo, he broadcast messages to the Greek people.

Paul returned to Greece in 1946. He succeeded to the throne in 1947, on the death of his childless elder brother, King George II, during the Greek Civil War (between Greek Communists and the non - communist Greek government). In 1947 he was unable to attend the wedding of his first cousin, Prince Philip, Duke of Edinburgh to the future Queen Elizabeth II of the United Kingdom as he was suffering from typhoid fever.

By 1949 the Civil War was effectively over, with the Communist insurgents ceasing the majority of their operations, and the task of rebuilding the shattered north of the country began.

In the 1950s Greece recovered economically, and diplomatic and trade links were strengthened by Paul’s state visits abroad. He became the first Greek Monarch to visit a Turkish Head of State. However, links with Britain became strained over Cyprus, where the majority Greek population favored union with the homeland, which Britain, as the colonial power, would not endorse. Eventually, Cyprus became an independent state in 1960.

In December 1959 Prince Maximillian of Bavaria presented the coronation regalia of King Otto of Greece to the King. It had been almost a century since they were last in Greece.

Meanwhile, republican sentiment was growing in Greece. Both Paul and Frederika attracted criticism for their interference in politics, frequent foreign travels, and the cost of maintaining the Royal Family. Paul responded by economizing and donated his private estate at Polidendri to the State.

In 1959, he had an operation for a cataract, and in 1963 an emergency operation for appendicitis. In late February 1964, he underwent a further operation for stomach cancer, and died about a week later in Athens.