The eldest of seven children, he is believed to have been born into a prosperous[6] country family from Pra Keap village, Trapeang Thom commune, Tram Kak district, Takeo Province, and was of Chinese-Cambodian descent.

Ta Mok orchestrated several massacres within the territories that he captured from 1973, beginning before the final, complete seizure of power by the Khmer Rouge on 17 April 1975.

For example, his and Ke Pauk's soldiers had 20,000 civilians murdered or forced into slave labour after capturing Oudong in March 1974.

[10] He was also responsible for directing the massive purges that characterised the short-lived Democratic Kampuchea (1975–1979), including the mass killing of 30,000 people in the Angkor Chey district, earning him the nickname Butcher.

Ta Mok was the last leading member of the Khmer Rouge to remain at large in Cambodia; other senior figures had died or already made immunity deals with the government of Hun Sen, including Nuon Chea, Khieu Samphan and Ieng Sary.

In poor health with respiratory problems, Ta Mok's only releases from solitary confinement were for hospital visits.

On 21 July 2006, due to heart complications caused by the stress of the upcoming trial, he died in a military hospital after falling into a coma.