Election of 65-year-old Rajendran at the end of the five-day conference was a "unanimous" decision of newly constituted 89-member state council of the party, CPI leaders said.
Though senior leader and former minister K E Ismail's name was suggested to the post by some leaders in the state council, he withdrew from the race following intervention of the national leadership, party sources said.
Ismail's decision not to contest the post paved way for the election of Rajendran who began his political career in 1970s as a student leader in Kottayam district.
"I will lead the party as a unified force. My immediate priority is to further strengthen the party in the state," said Rajendran, who is also the state president of the AITUC, the trade union wing of the CPI.
He dismissed reports that the CPI's Central leadership intervened to avoid a possible showdown between him and Ismail for the state secretary's post.
Reports had said there was strong difference of opinion between Rajendran and Ismail, both national executive members, and Ismail will contest against Rajendran for the secretary's post.
Ahead of the conference, Ravindran had announced that he was quitting the secretary's post.
