He was 88.
Kumar is survived by a son and a daughter.
Born in Jagdishpur village in erstwhile Shahabad district on November 23, 1926, Kumar had actively taken part in the freedom movement and was jailed by the British rulers.
A reputed leader of socialist background, he served as a member of the Bihar Legislative Council for four terms from 1962 to 1986.
Kumar held the position as a member of the Bihar State Backward Classes Commission from 1997 to 2008 and since then he was serving as a member of the Bureau of Parliamentary Studies and Training, Bihar.
Kumar's death has caused a huge void in public life, former chief minister and senior JD(U) leader Nitish Kumar said.
Earlier in the day, Kumar's body was brought to the state legislature premises where Manjhi and Awadesh Narayan Singh, besides a number of ministers and members of the two houses paid their tribute to the departed leader.