He entered the Calcutta District Committee after 1947, and also joined the editorial board of Swadhinata as a marxist intellectual (along with other radicals such as Saroj Dutta).
In May 1967, The non-Congress parties linked up to form the United Front coalition, (CPI-M along with CPI and the breakaway Bangla Congress).
At this time, Charu Majumdar, who had been involved with the peasant tribals of North Bengal, brought out some cyclostyled pamphlets calling for armed revolution.
A group of followers including Kanu Sanyal and Jangal Santhal lived and worked with the armed peasants, ousting landowners.
Sushital served as secretary and former Indian National Army activist Pramod Ranjan Sengupta was the president of the organisation.
On 12 November 1967, Sushital organized a two-day all India meeting of radical leftists at his house in Maniktala; Charu Majumdar flew down from Siliguri.
In November 1971, this dissident group formed a new Central Committee with Satyanarayan Singh as the General Secretary, and expelled Charu Majumdar.