Following the July 1951 assassination of Ḥussein's grandfather King ʿAbdullāh (Abdullāh Iʿ) in Jerusalem, his father, Ṭalāl, ascended to the throne but was in 1952 declared unfit to rule by parliament owing to mental illness. King Ṭalāl abdicated in favour of Ḥussein, who, after spending some months at Sandhurst Royal Military College in England, assumed full constitutional powers on May 2, 1953.

Ḥussein's policies fostered slow but steady economic progress, though he was forced to depend on significant financial aid from the West. Ḥussein's base of support was his country's indigenous Bedouin tribesmen, with whom he fostered close personal ties. The king's socially conservative policies and his alignment with the Western powers were often criticized by other Arab leaders as well as by his domestic opposition. Thus, popular demonstrations—especially among Palestinians who had fled to the West Bank after the 1948–49 war with Israel—and political unrest precluded his joining the pro-Western mutual defense treaty between the United Kingdom, Turkey, Iran, Pakistan, and Iraq, known as the Central Treaty Organization, or Baghdad Pact (1955), which he had helped initiate. In an effort to build domestic support, in 1956 he dismissed Gen. John Bagot Glubb (Glubb, Sir John Bagot), the British officer who commanded the Arab Legion (later part of a unified Jordanian army). Many Palestinians—who by that time represented a majority in Jordan—felt little attachment to his dynasty; Ḥussein responded by strengthening the military establishment to assert the authority of the crown over that of parliament.

With U.S. aid he steadily expanded and modernized his military forces, which he used to prevent attempts to overthrow his regime. Ḥussein reluctantly entered the Six-Day War of June 1967 (see Arab-Israeli wars), but Israel's military victory was a severe setback, resulting as it did in the loss to Israel of the West Bank and East Jerusalem, which Jordan had annexed in 1950, and the influx of some 250,000 additional Palestinian refugees into the country. After the war Ḥussein's rule was threatened by the military forces of the Palestine Liberation Organization (PLO), who based themselves in Jordan to carry out guerrilla raids against Israel. By September 1970 the PLO virtually controlled a state within a state. With his future in doubt, Ḥussein launched a full-scale attack to expel the organization in a civil war later remembered as Black September (see Jordan: From 1967 to civil war (Jordan)). Despite Iraqi and Syrian military support for the PLO, by August 1971 Ḥussein's army had succeeded in driving the PLO's forces from Jordan.

In the following years Ḥussein steered a difficult course: he refrained from confronting Israel militarily, mended relations with the PLO, and sought both closer ties with and financial aid from Saudi Arabia and other Arab states. He also maintained good relations with the United States and Great Britain. In 1988 Ḥussein surrendered Jordan's claim to the disputed West Bank, as well as its role in representing the Palestinians living there, to the PLO. Ḥussein walked a fine line during and after the events leading to Iraq's 1990 invasion of Kuwait and the Gulf War of 1991. While remaining sympathetic to Iraq brought popular domestic support for the king, the war cost Jordan dearly economically, as more than 300,000 Palestinians expelled from states in the Gulf region moved into Jordan. In the wake of the Israel-PLO accords of 1993, Ḥussein on Oct. 26, 1994, signed a bilateral peace treaty ending more than 40 years of hostility and normalizing relations between Jordan and Israel.

Ḥussein's autobiography, Uneasy Lies the Head, was published in 1962.