National election officer for organisational polls and former Bihar minister Ramchandra Purve announced Lalu's election at a meeting of the party's national council.
Lalu was the sole applicant for the post when he filed his nomination last Wednesday in the party office and was re-elected unopposed after his nomination was found valid.
Lalu has been holding the post since the party's inception in 1997.
Lalu's wife and former chief minister Rabri Devi, several senior RJD leaders and Union ministers, including Raghuvansh Prasad Singh, Prem Gupta and Jaiprakash Narain Yadav, state party president Abdul Bari Siddiqui were present at the meet.