Comrade Duch, the former head of the Khmer Rouge's notorious torture and execution prison known as S-21, was Monday sentenced to 35 years in jail at the UN-backed war crimes tribunal, dpa reported.
An estimated 20,000 people were tortured and condemned to death at S-21 as perceived enemies of the regime during the movement's rule of Cambodia between 1975 and 1979.
Duch, whose real name is Kaing Guek Eav, was charged with war crimes, crimes against humanity, and other crimes under Cambodian law.
In the closing days of his nine-month trial the 67-year-old stunned the court when sought acquittal on the grounds that international law did not apply and that he was merely following orders.
Around 1.7 million died from execution, overwork, starvation and disease under the Khmer Rouge regime.