"I will work to strengthen the party by taking along everybody with me in the same manner that you have unanimously entrusted me with the responsibility," he said addressing the party's national council meeting in New Delhi.
65-year-old Yadav made a fervent plea to keep the NDA alliance intact.
The election of Yadav, who is also the convener of NDA, came after an amendment in the party constitution, which earlier did not allow more than two terms to an incumbent as the party chief.
Yadav assumes the third stint as the JD-U chief at a time when there is intense speculation whether his party will remain with BJP-led NDA amid increased focus on Narendra Modi as BJP's prime ministerial candidate for 2014 Lok Sabha elections.
JD-U's aversion to Modi is a known fact, which has been given expression to many times by a number of party leaders and Bihar Chief Minister Nitish Kumar in particular.
Nitish Kumar proposed Yadav's name at the meet, which was endorsed. Yadav was the only one to have filed the nomination for the post and Saturday was the last day for withdrawal of papers.
Yadav's name was proposed by around 20 state units of the party including Bihar where JD-U is running a government in alliance with BJP. The Bihar chief minister was the first proposer in one of the nomination sets filed by Yadav.
Yadav became the JD-U president in 2006 succeeding George Fernandes who had been elected the party president in 2003.
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