Roy joined in Communist Party of India in 1963 and led trade union movements in Bansdroni area of Kolkata. After the seventh Congress in 1964, he joined Communist Party of India and mobilized group of workers against the imperialist Vietnam War. In 1966, Roy was at the forefront of the food movement of West Bengal, facing police atrocities and became arrested. After the Naxalbari uprising in 1967, Roy left the CPI. In 1980 he became the general secretary of erstwhile Maoist Communist Centre of India and the post he till kept in 1996. Roy also played a pivotal role in the unification of the M.C.C. with the Communist Party of India People's War Group in 2004. He inaugurated the United CPI. Roy was politically active in the state of Bihar and Jharkhand as Maoist ideologue and was considered to be the senior most leader of the CPI.