At least 1.7 million people died of disease, starvation or executions during the Khmer Rouge's reign between 1975 and 1979, with many survivors now fearing that some of the elderly defendants will die before they can be brought to justice.
The others awaiting trial are Khieu Samphan, the Khmer Rouge's former head of state; Ieng Sary, its foreign minister; his wife Ieng Thirith, who was minister for social affairs; and Nuon Chea, the movement's chief ideologue.
The date was set following a two-day meeting of judges and prosecutors in Cambodia.
"This is a very important and significant beginning for the court," Reach Saambath, a tribunal spokesman, said.
"We hope the work of the court will bring answers the public has demanded."
The trial before the Extraordinary Chambers in the Courts of Cambodia, as the tribunal is called, comes 30 years after the Khmer Rouge was toppled by a Vietnamese invasion.
It also comes 13 years after the tribunal was first proposed and nearly three years after the court was inaugurated.
The tribunal has been plagued by political interference from the Cambodian government, allegations of bias and corruption, lack of funding and bickering between Cambodian and international lawyers.