The decision was taken at CPI(M)'s three-day state committee meeting, which concluded today.
Mani, a first time legislator and CPI(M) state Secretariat member, is a veteran labour leader from the high range Idukki district and had functioned as the party's district secretary for many years.
He successfully contested the May 16 assembly polls this year from Udumbanchola.
Briefing reporters about the decision, CPI(M) state secretary Kodiyeri Balakrishnan said the party had decided to recommend Mani's name as minister as there was a vacancy following resignation of E P Jayarajan, the number 2 in the Pinarayi Vijayan cabinet.
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Asked about the portfolio which had been decided for Mani by the party, Kodiyeri said that was the prerogative of Chief Minister Pinarayi Vijayan.
The date of swearing-in and portfolio would be decided by the Chief Minister, he added.
Mani had stirred 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.
Speaking to reporters, Mani said he was very happy and was "indebted" to the party for the decision.
Asked about the portflio he had been alloted, Mani said that would be decided by the Chief Minister.
"My becoming minister was totally unexpected", he said.