He was 60 and is survived by his wife and two daughters.
Vijayan, a prominent figure in the state's CPI(M)-led Left Democratic Front (LDF), had been undergoing treatment for liver related diseases at Aster Medicity hospital since July 11.
He had been put on ventilator support for the last two days but died this morning, the hospital spokesman said.
Hailing from Uzhavoor in Kottayam district--the birthplace of former President K R Narayanan, Vijayan began his political career during his college days as a leader of the Kerala Students Union (KSU), the student wing of the Indian National Congress.
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He was a loyalist of NCP supremo Sharad Pawar, who had floated the Congress (S) after breaking away from the Congress.
Vijayan, known for his speech containing political wits, later joined the NCP and rose to the rank of its president.
He also emerged as a key member of the LDF state committee during the Assembly polls held last year.
His body will be kept at police ground at Kottayam today for paying homage.
His cremation will be held at 12 noon tomorrow at his village, NCP leaders said.