Thakur told reporters here that he has sent in his resignation to BJP national president Nitin Gadkari.
"I have resigned from the party post for several reasons, including ignorance and negligence as the state party president by the party leadership," Thakur said.
Thakur's son Vivek was denied ticket to contest the polls from Bankipur constituency.
Thakur's resignation comes a day before top BJP leaders were likely to start their poll campaign in Bihar.
Bihar will elect a 243-member assembly in staggered polling that begins Oct 21 and ends Nov 20. The results will be known Nov 24.
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