Sar Kheng was born on January 15, 1951, during the Sangkum in Ang Daung Saat Village, Krabau Township, Kamchay Mear District, Prey Veng Province.

[5] Along with Heng Samrin, Chea Sim, and Hun Sen, Sar Kheng was among the Democratic Kampuchea cadres of the Eastern Zone.

Human Rights Watch Asia Director Brad Adams described governmental policies that included imprisonment without trial and torture of political activists.

[14] A schism slowly developed in the CPP with Hun Sen and his supporters who would hold on to power at all costs on one side and the more moderate Kheng, Chea Sim and Heng Samrin on the other.

[17] Three years later, while planning the 1997 coup to oust his popular co-Prime Minister Prince Norodom Ranariddh, Hun Sen personally confronted Kheng to ensure his loyalty and support for the use of force.

This arrangement lasted until the Senate elections of 2006, when FUNCINPEC, which lost many seats while Ranariddh left to form his own party, dissolved the coalition and allied with Sam Rainsy's opposition movement.

In September 2015, he warned the authorities of Sihanoukville whom he suspected of taking bribes in return for allowing illegal fishing and smuggling activities off the coast.

[25] In 2019, Sar Kheng sued Sam Rainsy for his allegations that he had been colluding with Dy Vichea against Hun Sen, accusations which he considered "fake news and incitements".

In September 2015, Kheng announced the formation of a seven-person police commission to investigate the 2013 death threats made by CPP Interior Ministry official Lieutenant Colonel Pheng Vannak against CNRP deputy leader Kem Sokha.