"I have quit to facilitate the appointment of new President," Eshwarappa said, adding, he has sent his resignation letter to party president Rajnath Singh.
BJP sources said Eshwarappa, a prominent leader of the influential Kuruba community, had told the BJP leadership he was finding it difficult to manage the dual responsibilities of being a minister and party chief. Assembly polls are due in May.
65-year-old Eshwarappa had quit the erstwhile B S Yeddyurappa ministry in 2010 to take up the party post but returned to the Jagadish Shettar cabinet as Deputy Chief Minister and continued to head the party too.
Sources said senior BJP leader Arun Jaitley is expected to be here on Friday for consultations to appoint Eshwarappa's successor.