He was 79 and leaves behind his wife, three sons and two daughters.
Padayatt Kesavapillai Vasudevan Nair, popularly known as PKV, a four-time MP and leader of the CPI's parliamentary group in the Lok Sabha, breathed his last at 3.35 PM at the All-India Institute of Medical Sciences, where he was admitted last week after an infection in his lungs developed into pneumonia.
His condition worsened later after his kidneys stopped functioning following which he underwent dialysis twice, CPI secretary D Raja said.
Born in Kidangur village in Kottayam district of central Kerala, PKV had his baptism in politics during his student days as an activist of the All-India Students Federation (AISF).
The initial years were tumultous as the AISF, which was a part of the then undivided Communist Party of India (CPI), was fighting against British imperialism.
PKV, who represented Thiruvananthapuram constituency in the Lok Sabha, soon plunged into active politics when he joined the CPI in 1945 while he was still in college.
The subsequent years saw him evolve as a student and youth leader when he was elected president of the Travancore Students' Union in 1947 and president of the Students Federation in 1948.
After the announcement of the "Calcutta Thesis", which called for militant uprising to overthrow the national government in 1948, prompting the government to ban the Communist Party, he went underground along with hundreds of his party colleagues. Nair also served as editor of Janayugom daily, the organ of the CPI between 1954-57.
He won his first electoral battle in 1957 when he gained entry into the Lok Sabha from the Tiruvalla constituency. He later won from Ambalappuzha in 1962 and from Peermade in 1967.
Known for his unpretentious and down-to-earth nature, he remained with the CPI after the party split in 1965 and went on to become the Chief Minister of Kerala in 1978.
After a long parliamentary career, Nair returned to state politics in the 1970s and was elected to the Kerala Assembly in 1977 in the polls held after the Emergency.
He was the Industry Minister in the Karunakaran and Antony ministries from April 1977 to October 1978.
A K Antony resigned in 1979 protesting against the Congress choice of Indira Gandhi as a candidate in Chikmagalur, PKV became Chief Minister with the support of the Congress on October 29, 1978. He, however, resigned after a year when the CPI decided to snap its ties with the Congress and work in cooperation with the CPI-M and other Left parties.
His body would be kept at the party headquarters here tomorrow for his colleagues and workers to pay their last respects before being flown to his native village for cremation.