The JD-U faction led by Bihar Chief Minister Nitish Kumar on Saturday joined the National Democratic Alliance (NDA) at the party's national executive meeting in Patna.
"A resolution that the JD-U will join the BJP-led NDA was unanimously approved in the meeting," a senior party leader said.
According to the leader, Janata Dal-United General Secretary K.C. Tayagi moved the resolution, which was approved by all invited members.
However, a formal announcement in this regard has not been made.
"K.C. Tayagi will announce it formally at a press meet after the meeting is over," the party leader told IANS.
The meeting began at the official residence of Nitish Kumar, who is also the JD-U president.
Most of the JD-U leaders, including 70 party MLAs, two Lok Sabha MPs and seven Rajya Sabha MPs also participated.
It is a major decision in the party after Nitish Kumar last month dumped the RJD-Congress and joined hands with the BJP to form a new government in Bihar.
The JD-U now has two factions: one led by Nitish Kumar and the other by senior party leader and former party president Sharad Yadav.
