He was exiled to Corsica by French authorities on 20 August 1953, along with his father Sultan Mohammed V. They were transferred to Madagascar in January 1954. Prince Moulay Hassan acted as his father's political advisor during the exile. Mohammed V and his family returned from exile on 16 November 1955.
Prince Moulay Hassan participated in the February 1956 negotiations for Morocco's independence with his father, who later appointed him Chief of Staff of the newly founded Royal Armed Forces in April 1956. In the unrest of the same year, he led army contingents battling rebels in the mountains of the Rif. Mohammed V changed the title of the Moroccan sovereign from Sultan to King in 1957. Hassan was proclaimed Crown Prince on 19 July 1957, and became King on 3 March 1961, after his father's death.
In the early 1970s, King Hassan survived two assassination attempts. The first, in 1971, was organized by General Madbouh and Colonel Ababou and carried out by cadets, during a function at Skhirat, an ocean resort. On August 16, 1972, during a second attempt at a coup d'état, jets from the Royal Moroccan Air Force fired upon the King's Boeing 727 while he was traveling back to Rabat, but failed to bring it down. General Mohamed Oufkir, Morocco's defense minister, was the man behind the coup and was officially declared to have committed suicide after the attack. His body, however, was found with several bullet wounds.
In the Cold War era, Hassan II allied Morocco with the West generally, and with the United States in particular. There were close and continuing ties between Hassan II's government and the CIA, who helped to reorganize Morocco's security forces in 1960. Hassan served as a back channel between the Arab world and Israel, facilitating early negotiations between them. This was made possible due to the presence in Israel of a large Moroccan Jewish community.
During his reign, Morocco recuperated the the Spanish-controlled area of Ifni in 1969, and seized two thirds of Spanish Sahara (now Western Sahara) through the "Green March" in 1975. The latter issue continues to dominate Moroccan foreign policy to this day. Relations with Algeria have deteriorated sharply due to the Western Sahara affair, as well as due to Moroccan claims on Algerian territory, which unleashed the brief 1963 Sand War.
Economically, Hassan II adopted a market-based economy, where agriculture, tourism, and phosphates mining industries played a major role.
King Hassan II had extended many parliamentary functions by the early '90s and released hundreds of political prisoners in 1991, and allowed the Alternance, where the opposition assumed power, for the first time in the Arab World. He set up a Royal Council for Human Rights to look into allegations of abuse by the state.
The king also had one other wife, Lalla Fatima bint Qaid Amhourok. Married also in 1961, they had no children.