Political career

Mani practiced as a lawyer before entering into politics as an active member of Indian National Congress. He served as the Kottayam DCC (District Congress Committee) Secretary from 1960 till the formation of Kerala Congress in 1964. He was elected to Kerala Legislative Assembly for the first time in 1965 from the Palai Assembly Constituency (now PALA) Constituency of Kottayam district, and since then he won all the ten elections that followed in 1967, 1970, 1977, 1980, 1982, 1987, 1991, 1996, 2001 and 2006. He was minister for Home Affairs (April 1977 to September 1978 and again from October 1978 to July 1979), Finance and Law (January 1980 - October 1981, December 1981-March 1982 and again from May 1982-March 1982-March 1986), Irrigation and law(1987), Revenue and Law(1987), Revenue and Law (June 1991 to March 1996),Revenue and Law(2001 to 2006). He has never lost an election to the Legislative Assembly.
He lost the Chief Minister post of Kerala in 1979 twixt cup and lip when P K Vasudevan Nair resigned. Then C. H. Mohammed Koya became Chief Minister and after 2 months Mani withdrew his party's support on that government and C. H. resigned. Again Mani got a chance to become the Chief Minister, but with the interference of Congress party the Assembly was dissolved in favour of all those who did not wish him to become the Chief Minister.
In the faction ridden Kerala Congress, Mani is accused by political foes as having engineered many a split in the party. He is also famous for describing the Kerala Congress as a party "which splits as it grows and grows as it splits".
In his tenure as being a Member of the Legislative Assembly (MLA), he is second only to K. R. Gowri Amma.
In a public function organised at Ramapuram, Palai on October 2009, M. M. Jacob, senior Congress leader and former Meghalaya Governor said that he advised Mani in 1965 to contest in the Congress party label and if it was done Mani would have become the Chief Minister very early. Again he said that now Mani is fully eligible for the post of Chief Minister.
In 2009, Mani got the P. R. Francis award for the best social worker of Kerala. After presenting the award to Mani in a function organised at Thrissur, Congress leader Oommen Chandy invited him to Congress party. But Mani rejected.
On November 2, 2009, P. C. George faction of the Kerala Congress decided to merge with Kerala Congress (M). This was a major breakthrough in the Kerala politics since George abused and criticised Mani for many years.
On 30th April 20, P. J. Joseph resigned his ministerial post and declared that his Kerala Congress is going to merge with Kerala Congress (M). Political analysts have estimated that this decision will help Kerala Congress to sweep almost all the assembly seats in Central Travancore region and will create a new diversion in Kerala politics.