Khieu Samphan was born July 27, 1931 in Svay Rieng Province, Cambodia; the son of a judge.
He studied economics at Paris University, graduating with a doctorate degree in 1950; returned to Cambodia in 1959, taught as a member of the law faculty of the University of Phnom Penh, and published a left-wing French-language newspaper, L'Observateur. The paper soon acquired a reputation in Phnom Penh's small academic circle, in which the right-wing dominated government and Phnom Penh's establishment felt threaten. The following year, the government closed the newspaper, and Khieu Samphan was publicly humiliated by police; he was undressed and photographed in public. It was a kind of humiliation, as William Shawcross notes "not the sort of humiliation that men can forgive or forget."
Although experience the humiliation, it did not prevent Khieu Samphan from advocating cooperation with Prince Sihanouk's Sangkum (government) in order to promote a united front against United States activities in South Vietnam. In June 1962 Khieu Samphan was elected as deputy to the National Assembly, and accepted a government post as state secretary in the Ministry of Commerce. In February 1963 riots broke out in Siem Reap province, which caused largely by the antagonism that had been building for some time between students and the police. Prince Sihanouk blamed the left for the violence which in March he released a list of 34 'subversives' whom he said were working to bring down the government. Five leftist member of the Sangkum who held seats in parliament, including Khieu Samphan, where on the list. As the result, he left the cabinet but continued as members of parliament.
In early 1967 a peasant rebellion erupted in Samlaut in northwestern Cambodia; Lon Nol's government brutally suppressed the revolt, in which Lon Nol was forced to resign the Premiership. Meanwhile, Prince Sihanouk's alarm over the revolt threatened to arrest the former Sangkum leftists for alleged inciting the revolt; as a result, Khieu Samphan and his associates - Hu Nim and Hou Youn - had all disappeared by October. At the time of their disappearances, the three were presumed to have been murdered by police.
In 1970 he became deputy prime minister and minister of defense in the Royal Government of National Union of Kampuchea (RGNUK), a government-in-exile which was formed by Prince Norodom Sihanouk in May, and commander-in-chief of the People's Army of National Liberation of Kampuchea.
The Khmer Rouges captured Phnom Penh on April 17, 1975. Immediately after its victory, the Khmer Rouge ordered the evacuation of all cities and towns, sending the entire urban population out into the countryside to till the land. Thousand starved or died of disease during the evacuation; the forced evacuees were resettled in new villages, which lacked food, agricultural implements, and medical care; many starved before the first harvest.
On April 4, 1976 Prince Sihanouk who returned to Phnom Penh in September 1975, resigned as head of state, and was placed under house arrest. Late that month, Pen Nouth resigned from his Premiership. On April 14, 1976 at its first session, the People's Representative Assembly confirmed Khieu Samphan as President of the State Presidium (Head of State) of Democratic Kampuchea. It also selected a 15-member cabinet headed by Pol Pot as Prime Minister.
Democratic Kampuchea's relations with Vietnam and Thailand worsened rapidly as a result of border clashes and ideological differences. Border clashes worsened when the Khmer Rouge attacked Vietnamese villages; in mid-1978 Vietnamese retaliated by invading about 30 miles into Cambodia, and on December 25, 1978, Vietnamese forces launched a full invasion of Cambodia, capturing Phnom Penh on January 7, 1979, and driving the Khieu Samphan's government westward toward Thailand. A new government, People's Republic of Kampuchea, headed by Heng Samrin former Khmer Rouge military commander, was established to replace Democratic Kampuchea.
By mid-1979 the Khmer Rouge's carnage emerged and the unspeakable atrocities became known to the world. Khieu Samphan and the Khmer Rouge became international pariahs. However because of cold war antagonistic between the east and west, in which Cambodia was unfortunately caught in the middle, many governments continued to support the murderous regime. The Chinese government started arms shipments via Thailand in February 1979. And in mid-September their sympathizers secured them a voice at the UN. The Khmer Rouge continued to represent Cambodia at the UN. And in December, in an attempt to improve its image, Khieu Samphan was appointed as Prime Minister of Democratic Kampuchea, replacing Pol Pot who was appointed as Commander-in-Chief of the armed forces.
In June 1982, a united front of the three Cambodian rebel factions (the Khmer Rouge, FUNCINPEC of Prince Norodom Sihanouk, and Khmer People's National Liberation Front of former Prime Minister Son Sann) agreed to form a government-in-exile "Coalition Government of Democratic Kampuchea" with Prince Sihanouk as President, Khieu Samphan as Vice-President in charge of Foreign Affairs, and Son Sann as Prime Minister.
In 1986, Vietnam claimed to have begun withdrawing part of its occupation forces and continued until September 1989. The PRK and CGDK started negotiation for peace. From July 30 to August 30, 1989, representative of 18 countries, the four Cambodian warring factions, and the UN secretary-general met in Paris in an effort to negotiate a comprehensive settlement, which was signed on October 23, 1991. The agreement given UN full authority to supervise a cease-fire, repatriate the displaced Cambodians, disarm and demobilize the factional armies, and to prepare for a free and fair election.
On November 27, 1991 Khieu Samphan returned to Phnom Penh. Within hours mayhem had broke loose, and a mob attacked him in his villa. The bloodied Khmer Rouge leader headed back to the airport and left the country. During 1992, the Khmer Rouge refused to demobilize their fighters as required by the Paris Accord; by the beginning of 1993 the Khmer Rouges started to pull out from the peace accord and fought for land.
The UN supervised elections were held in September 1993 without Khieu Samphan's faction participation. A new government was formed and a new constitution was promulgated in September 1993. In June 1994 the government closed Khmer Rouge offices in Phnom Penh; the National Assembly outlawed the Khmer Rouge and offered a six-month amnesty to rank and file guerrillas. By the time the amnesty period was up in January 1995, some 7,000 Khieu Samphan's soldiers had reportedly defected to the government. The Khmer Rouge broke apart in August 1996 when Ieng Sary (the Khmer Rouge foreign minister) defected to the government with a huge number of troops.
On December 25, 1998 Khieu Samphan with Nuon Chea surrendered to the Cambodian government; they were warmly received by the government leader and allowed to live free in the semi-autonomous region run by Ieng Sary.