Bersani told a meeting of parliamentarians he would quit as Democratic Party (PD) leader as soon as the election of the next head of state was completed, following two dramatic days of parliamentary voting in which successive center-left candidates were scuppered in secret ballots.
"He accepted his responsibility after the disgrace of what happened," Paolo Gentiloni, a senior Democratic Party parliamentary deputy said after Bersani's announcement.
Then disarray in the center-left, which has the most seats in parliament, could make a snap election in the summer more likely to end the political deadlock, but there is no clarity about the next moves after weeks of chaos.
It is unclear who will take over leadership of the badly split party but Bersani's departure could clear the way for arch-rival Matteo Renzi, the dynamic 38-year-old mayor of Florence, to take over.
Bersani's announcement came shortly after former Prime Minister Romano Prodi announced he was pulling out of the race for president after more than 100 center-left electors disobeyed Bersani's instructions to vote for him in parliament.
It was the last of a series of humiliating setbacks for Bersani and blunders that have shredded his ability to hold the center-left bloc together.
The collapse of efforts to secure the presidency for Prodi, a respected international figure, underlined the deep fractures running through politics in a country still seeking a government nearly two months after February's inconclusive general election.
"The politicians should be ashamed of what they're doing to the country. Today we're seeing a level of irresponsibility that goes beyond all limits," said Diego Della Valle, head of shoe group Tod's, one of Italy's most successful clothing companies.