One of the prime organisers of the Bengal Provincial Committee of the All India Students Federation, which split later in 1964 following ideological battle against revisionism, he along with the major fraction of the Bengal Provincial Committee took a leftist stand and the fraction came to be known as the BPSF (Left) or SF(Left).

He married fellow SF(Left) leader Shyamali, who later became a member of CPI(M) Central Committee, and the All-India President of the All India Democratic Women's Association.

As BPSF leaders, they took active role in organizing protest rallies against the Vietnam War in the sixties, and expressed solidarity with the Vietnamese people's struggle for liberty and socialism.

Even during the times of Naxal terror, he remained in Siliguri and continued to inspire the students, and organized the university teachers' movement.

In 1977, when Jyoti Basu became the Chief Minister of the 1st Left Front Government, Sankar Gupta was asked to be his Political Secretary.