JD(S), a partner in the ruling CPI(M)-led LDF in Kerala, has three MLAs in the state assembly.
Nadar was elected as the new president of the party's state committee as the outgoing president Mathew T Thomas has joined as Water Resources Minister in the Pinarayi Vijayan-led ministry, Deve Gowda said in a release.
George Thomas was elected as the new secretary of the committee, the release said.
A two-time minister, Nadar had held the portfolios of Sports and Youth Affairs and Forest and Transportation in the state assembly during 1987-1991 and 1999-2000, respectively.