Singh was found hanging in his Tihar Jail cell about 5 a.m. sources told the Press Trust of India.
India TV reported jail officials said Singh used his shirt to hang himself from the grills of his cell. He was taken to a hospital but was declared dead on arrival.
Singh and four other defendants were to have been brought before the fast track court Monday, India TV said.
The Hindustan Times said Singh, the 33-year-old driver of the bus where the victim, a college student, was raped and her boyfriend beaten Dec. 16, faced 13 criminal charges that could have resulted in him receiving the death penalty if convicted.
The Times said authorities considered him the one who instigated the brutal attack.