Hospital sources said Pankajakshan (84), who was also a former Kerala Minister, died due to old-age related problems.
Panjakshan is survived by his wife, two sons and one daughter.
He was admitted to the hospital four days ago.
Pankajakshan was one of the senior most politicians in the state and was a member of Kerala assembly from 1970 to 1991.
He had also served as a minister in five Kerala cabinets.
Various political leaders of the state condoled the death of Pankajaskhan.
CPI-M veteran and state Opposition leader V S Achuthanandan said the death of Pankajakshan was a "great loss" to the Left movement in the country.