RCP Singh, a close confidant of Bihar Chief Minister Nitish Kumar, was on Sunday chosen as the new president of Janata Dal (United).
Kumar had proposed the name of Singh for the top post, which was then approved by other members during the party's national executive meeting, a senior leader told PTI.
The chief minister, who was re-elected as the JD(U) president in 2019 for three years, relinquished the post in favour of Singh, its leader in Rajya Sabha.
Singh, a bureaucrat-turned-politician, was so far the general secretary of the regional party.
The JD(U) is holding its national executive meeting to deliberate on issues related to the country's political situation after six out of the party's seven MLAs switched over to the BJP.
Polls in neighbouring West Bengal also came up for discussion at the meeting, the senior leader said.