In August 1953 a joint CIA-MI6 operation (TPAJAX / Ajax) overthrew Iran's elected Prime Minister Mohammad Mossadegh, who had nationalised Iranian oil; the young Shah returned from a short exile in Rome. For the next 25 years the Shah, a close US ally, drove an accelerated programme of modernisation called the "White Revolution": land reform, the vote for women (1963), literacy corps, industrialisation and, after the oil-price rise of the early 1970s, an economic boom. In the same years the intelligence service SAVAK harshly suppressed political, leftist and religious opposition. The Shia cleric Ruhollah Khomeini, exiled in 1963 for opposing the White Revolution, directed the movement from Najaf (Iraq) and then from Neauphle-le-Château outside Paris — by smuggled cassette tapes and through journalists on Air France flights.

Through 1978 the crisis escalated. In January, police fired on a demonstration of religious students in Qom; the traditional forty-day mourning cycle chained the protests together. On 19 August 470 people died in the Rex Cinema in Abadan (responsibility remains contested; the doors had been locked from outside). On Black Friday, 8 September, the army fired into the crowd on Jaleh Square; the death toll is still debated (88 to several hundred). The oil workers' strike paralysed the economy in late October. In December, between one and two million people joined the Ashura processions in Tehran — one of the largest demonstrations in modern world history. On 16 January 1979 the Shah and Farah Pahlavi left Mehrabad airport "on holiday"; the photograph of a general kneeling to kiss the ground at the airport became a symbolic closing image. On the morning of 1 February Khomeini's Air France 4721 landed in Tehran; through the millions who filled the airport area he moved by helicopter to Behesht-e Zahra cemetery. "This government appointed by the Shah is illegitimate," he said, and he named Mehdi Bazargan provisional prime minister. For ten days the Shah's last prime minister Shapour Bakhtiar and Bazargan ran parallel governments. On 9-10 February air-force technicians (homafars) declared loyalty to Khomeini; on the afternoon of 11 February the Supreme Military Council announced that the army would remain neutral; the Bakhtiar government collapsed.

In the referendum of 30 March-1 April, 98 per cent voted for an "Islamic Republic" (the only option on the ballot). In December 1979 the new constitution, built on Khomeini's doctrine of velayat-e faqih (guardianship of the jurist), was adopted: above the elected president and parliament sat a Supreme Leader and clerical oversight bodies (the Guardian Council, the Assembly of Experts). On 4 November 1979 students stormed the US embassy; 52 Americans were held for 444 days — the crisis decided Carter's defeat in 1980, and diplomatic relations between Tehran and Washington remained broken into the 2020s. In September 1980 Saddam Hussein's Iraq invaded Iran; eight years of war, more than a million dead and the use of chemical weapons made it one of the bloodiest conventional wars of the 20th century. In the same period the revolution purged secular liberals, the Tudeh communists and the People's Mojahedin from within; thousands of political prisoners were executed (notably in the mass executions of 1988).

The international impact has been wide. The revolution opened the redrawing of the Sunni-Shia axis: Saudi Arabia accelerated its Wahhabi counter-projects, Hezbollah was born in Lebanon in 1982, Shia movements revived in Bahrain and Eastern Arabia. In Cold War terms the Carter Doctrine (January 1980) declared the Gulf a vital US interest; that same year the Soviets invaded Afghanistan, partly out of border anxiety created by the Iranian Revolution. The revolution also showed the world that the classical theory linking modernisation to secularisation might be wrong; the rise of religion-based political movements from Turkey to India, from Poland to the United States, has been a global pattern since the 1980s. Inside Iran, the system created by the revolution has lived with both persistent legitimacy crises (the 2009 Green Movement, the economic protests of 2017-18 and 2019, the 2022 "Woman, Life, Freedom" movement) and Tehran's central role as a regional power. On the Eon timeline, February 1979 is a doubled moment: the closing of the account opened by the 1953 coup, and the drawing of the frame for the next half-century of the Middle East.