Kumar became the general secretary of the RCPI (Pannanlal Dasgupta group) at the All India Conference held in Howrah in 1960.
[3] Kumar served as convenor of the United Front formed ahead of the 1967 West Bengal Legislative Assembly election.
[7][5] After the 1969 West Bengal Legislative Assembly election Kumar was named Food and Supplies Minister in the second United Front state government.
[4][8][9] The Food Minister had been given to the Communist Party of India (Marxist) in the coalition government, but CPI(M) opted to name Kumar as its choice for the post.
[18] However, in the subsequent 1972 West Bengal Legislative Assembly election Kumar lost the Howrah Central seat to Mrityunjoy Banerjee.
[21][22] Kumar lost the Howrah Central seat to Congress(I) candidate Ambica Banerjee in the 1982 West Bengal Legislative Assembly election.