Veerendra Kumar announced his decision to resign from the Upper House after sending a resignation letter to Rajya Sabha Chairman M Venkaiah Naidu.
"Legally, I'm in Rajya Sabha as a member of Nitish Kumar's party. I don't agree with his stand dumping the 'Mahagathbandhan' and alingning with the Sangh Parivar and the BJP," he said in a press conference here.
On the recent Gujarat state elections, Veerendra Kumar said what happened in Gujarat was not a victory for Prime Minister Narendra Modi.
The rebellion in the JD(U) started after Nitish Kumar, the Bihar chief minister, decided to break ranks with the Rashtriya Janata Dal and the Congress in Bihar and join the NDA in July.
Veerendra Kumar, a media baron from Kerala and the JD(U) state unit president, had last month announced his decision to relinquish his Rajya Sabha membership amid the political crisis gripping the party at the state-level.
JD(U) leader Sharad Yadav was recently disqualified as a member of the Upper House after Naidu agreed to his party's plea that he had "voluntarily given up" his membership by joining a rally of opposition parties in Patna in August.