He entered politics through trade union activities and joined State Congress in 1938. In 1940, he became a member of the Communist Party of India (CPI) [citation needed]. During his 40 years as a politician he was imprisoned for five years and six months[citation needed] and had gone under hiding for four and half years. He was a state secretariat member of the CPI in 1957. During the Sino-Indian war in 1962, he was with the nationalists in the party, supporting Indian side. He was demoted in the party rank when he participated in a blood donation camp to help Indian soldiers. He is the only one living Keralite among the 32 members who left the CPI National Council in 1964 to form the CPI(M). He is the senior most leader of CPI(M) in Kerala.
The anti-reclamation stir launched by the Kerala State Karshaka Thozhilali Union (KSKTU) at Mankonpu in 1996-97, under the leadership of Achuthanandan created much controvesy. The protest got the sobriquetvettinirathal samaram following the violent methods and crop destruction resorted to by the KSKTU cadre. The stir generated lot of public criticism and Achuthanandan expressed his disapproval of any further destruction of crops.He was active in the famous Punnapra-Vayalar uprising that led to a police shootout killing many.
