VS Achuthanandan was the Chief Minister from 2006 to 2011.
VS Achuthanandan, the veteran Communist Party of India-Marxist (CPI-M) leader and also a former Chief Minister of Kerala, turned 96 on Sunday making him one of the country's oldest politicians.
A seven-time legislator, Mr Achuthanandan represents the Malampuzha Assembly constituency in Palakkad district.
He had campaigned for the 34-year-old Thiruvananthapuram Mayor, VK Prasanth, the CPI-M's candidate for the prestigious Vatiyoorkavu assembly constituency, which is going to elect a new legislator on Monday.
Mr Achuthanandan was the Chief Minister from 2006 to 2011.
He is also the incumbent chairman of the Administrative Reforms Commission, which has a cabinet status position.