He was an active member in
SFI, holding posts like unit secretary of
Sree Kerala Varma College,
Chelakkara area secretary, and member of Thrissur district secretariat as an SFI leader. He also worked as Chelakkara Block Committee secretary and state committee member of
DYFI, and he is now CPI(M) central committee member. Radhakrishnan was elected to the
Thrissur District Council in 1991 from the Vallathol Nagar division. He was elected to the
Kerala Assembly in 1996, 2001, 2006, 2011 and 2021. He served as Minister for the Welfare of Backward and Scheduled Communities and Youth Affairs from 1996 to 2001. He was Opposition Chief Whip from 2001 to 2006. He was District Secretary of CPI(M), Thrissur from 2016 to 2018. He was also District Convenor of
Left Democratic Front, Thrissur from 2013 to 2018. He was the founder State President of the CPI(M) Kerala-controlled Pattikajathi Kshema Samithi (Eng. Scheduled Castes Welfare Committee), briefly known as "PKS", which is a welfare committee for scheduled castes of Kerala. He also served as the State President of Farm Workers Union (
CITU), Kerala Clay Pottery Workers Union. He was elected to
CPI(M) Central committee on 22nd Party Congress held on 2018.{{cite news|url=http://www.hindu.com/2004/04/29/stories/2004042910000400.htm ==Electoral record==