He has been the longest-serving minister in the Government of Kerala to date and continuously represented Pala legislative constituency since its inception in 1965 until his death in 2019.

According to him, farmers, agriculture labourers and other workers belong to the category of working class and they should stand together to ensure their rights.

The significance of Mani was that even the Left was forced to accept this theory when it decided to bring farmers in to their fold.

[citation needed] He lost the Chief Minister post of Kerala in 1979 when P. K. Vasudevan Nair resigned.

On 10 November 2015, Mani was pulled down from the position as Minister of Finance and Law Kerala state, as he was accused of being a part of bar bribery scam.

He was the Chairman of the Empowered Committee of State Finance Ministers on Goods and Services Tax (GST).

He is the author of Fiscal Problems of Kerala – Causes and Remedial Measures, The People's Socialism, and The Eighth Five Year Plan – An alternative approach.

He presented paper on India and Globalisation: Asian Economic Community – Need of the Day at the National Seminar held in New Delhi on 22 December 1994.

[4] He died on 9 April 2019 in Lakeshore Hospital, Kochi due to chronic obstructive pulmonary disease.