Mani, a state Secretariat member of CPI(M) and first-time MLA, represents Udumbanchola constituency in the hilly Idukki district. He is likely to be sworn in on November 22.
He has also served as the party's Idukki district secretary for many years.
Party state secretary Kodiyeri Balakrishnan made the announcement after a three-day state committee meeting, which ended today.
Kodiyeri told reporters that the party had recommended induction of Mani as there was a vacancy following resignation of Industries Minister E P Jayarajan, who was the number two in the cabinet.
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Asked which portfolio will be given to Mani and when will he be sworn-in, Kodiyeri said it will be decided by the Chief Minister.
Mani had earlier stirred a controversy by his statement that CPI(M) had often eliminated its political foes in Idukki district in the 1980s, following which police had registered a case against him for murder and other charges.
He was arrested in November 2012 in connection with the case registered for murder of Anchery Baby, a Youth Congress leader, who was shot dead on November 13, 1982.
"My becoming minister was totally unexpected," he said.