Singh was on a morning walk when he was accosted by gunmen who pumped several bullets into him, killing him on the spot at Katira Mohalla under Nawada police station, 71 kms from Patna, they said.
Singh alias Mukhiya ji, who was earlier facing life imprisonment in various carnage cases, was acquitted and released from jail in April this year.
Chief of Ranvir Sena, a private militia of upper caste landlords, is allegedly responsible for perpetrating several killings including Laxmanpur Bathe massacre of 61 Dalits way back in December 1996.
His hand was also suspected in carnages that took place in the districts of Jahanabad, Aurangabad and Nawada in 1990s.
As the news of the killing spread, hundreds of Sena supporters gathered at the site of the killing and shouted anti-government slogans. They also tried to chase away policemen including the superintendent of police, who had arrived at the spot.
Patrolling has been intensified in the area as tension ran high.