Chan Sy was born in 1932 in Kompong Chhnang Province, Cambodia.
He joined the Khmer Viet Minh forces in 1950s, left Cambodia in 1954 after the Geneva Conference that recognized Prince Norodom Sihanouk's government as the sole legitimate authority in independent Cambodia.
A member of the Communist Party from 1960, Chan Sy was believed to have returned to Cambodia in 1970 after the coup that ousted Prince Sihanouk and placed the pro-U.S. Lon Nol in power.
Chan Sy, who was opposed to ultra-nationalist Pol Pot, by whose partisans he was detained in 1973 and disappeared....... He reappeared on the scene in 1978, with the forces of the Kampuchean United Front for National Salvation (KUFNS) and with the Vietnamese that toppled the murderous Khmer Rouge regime in 1979.
After some months of military training in the Soviet Union, in 1980 he was appointed deputy defense minister and following year defense minister and vice-president of the Council of Ministers; the same year he also became a member of the Politburo of the Kampuchean People's Revolutionary Party (KPRP).
When Pen Sovan was replaced as party secretary-general by Heng Samrin, Chan Sy took over the premiership. Considered a steadfast adherent to Vietnam's Kampuchean policy, Chan Sy had made visits to Bulgaria and East Germany as well as to the U.S.S.R. In the Nation Assembly he represented his native province.
Chan Sy died in a Moscow hospital, where he was being treated for a cardiac ailment, in December 1984. His death was reported by the Vietnamese information agency on December 31, 1984; he was believed to have died some days earlier.
Source: Britannica Book of the Year 1985