The 78-year-old Sanyal was found hanging at his residence at Seftullajote village, 25 kms from Siliguri, police said.
According to police, Sanyal was suffering from old age related ailments.
"The body has been sent for post-mortem," Inspector General of Police (North Bengal) K L Tamta said.
Sanyal was a founder of the Communist Party of India (Marxist-Leninist) formed in 1969.
Sanyal, along with Charu Majumdar, started the movement from Naxalbari, a small village in North Bengal on May 25, 1967.