Manjhi, who was expelled by the JD (U) earlier this month, had so far refused to resign and had insisted that he had the support to remain chief minister.
Manjhi sprang a surprise by making an unscheduled visit to Raj Bhawan around 10 AM. He returned to his One Anne Marg residence after a brief 15-minute meeting with the Governor.
Manjhi's sudden decision apparently follows his realisation that he does not have the numbers to prove the majority. He added that he did not get respect as chief minister.
"I have submitted my resignation letter to the governor. I should have quit before," said Manjhi soon after he met the Governor.
He also claimed that he as well as some legislators had received threats to their lives.
Manjhi is also said to have recommended the dissolution of the Bihar assembly too.
The Bharatiya Janata Party (BJP) had decided to vote with the Manjhi faction in the confidence vote, hoping that this will win it support from the state's sizeable ‘Mahadalit' community.
BJP state unit chief Sushil Kumar Modi had said on Thursday the legislative party will vote in favour of Manjhi. Sources said all 87 BJP MLAs were unanimous that the party should back Manjhi.
Nitish Kumar has claimed the support of 130 MLAs. This includes MLAs of JD(U), RJD, Congress and Left parties.
Responding to Manjhi's resignation, Kumar said the BJP's game plan has been exposed.