'GREAT SADNESS'
In a statement, Corzine said his "difficult" decision was voluntary, and was best for the company and its stakeholders.
"I feel great sadness for what has transpired at MF Global and the impact it has had on the firm's clients, employees and many others," Corzine said. "I intend to continue to assist the company and its board in their efforts to respond to regulatory inquiries and issues related to the disposition of the firm's assets."
Corzine is not seeking severance, the company said. He had been entitled to a $9 million payout if he were let go without cause, a July regulatory filing shows.
MF Global said Chief Operating Officer Bradley Abelow and lead director Edward Goldberg will remain in their positions.
The company's bankruptcy is the seventh-largest in U.S. history, according to BankruptcyData.com and Reuters data. A trustee plans to liquidate MF Global's U.S. broker-dealer unit.
LAWYERS HIRED AS REGULATORS ZONE IN
Brokerages such as MF Global are required to keep customer money segregated from their own cash.
Questions about whether MF Global failed to do this have attracted the attention of the Federal Bureau of Investigation as well as regulators.
Corzine has hired prominent white-collar defense lawyer Andrew Levander of the law firm Dechert to represent him in cases that might stem from the bankruptcy filing, a legal source briefed on the matter said on Thursday.
Levander has represented outside directors of Lehman Brothers Holdings Inc and former Merrill Lynch & Co chief John Thain, among others. Corzine hired another lawyer, Schuyler Carroll of Perkins Coie, for the bankruptcy case.
"We will look at every aspect of how the firm conducted business," Mary Schapiro, chairman of the U.S. Securities and Exchange Commission, told Reuters on Thursday.
SURPRISE HIRE
Corzine's decision to join MF Global surprised many on Wall Street at the time.
He has referred to himself as a "recidivist banker," saying that financial regulatory reform would force big banks to shrink, leaving growth opportunities for potential rivals that were "too small to care about."
One of the biggest market concerns about MF Global had been its roughly 33-to-1 leverage ratio, with well in excess of $40 billion of assets despite having just $1.4 billion of equity.
Going into the 2008 financial crisis, some of Wall Street's biggest companies had had similar leverage, and Corzine has called that risk unacceptably high.
Last month, before MF Global's collapse, Corzine spoke with a group of equities traders in New York and said that his perspective had changed.
"He said Wall Street needs more clarity about the rules and better incentives for doing business and taking risk," said a person who attended the off-the-record event organized by the National Organization of Investment Professionals.
(Reporting by Jennifer Ablan, Matthew Goldstein, Jed Horowitz, Jennifer Merritt and Jonathan Stempel in New York; Editing by Derek Caney and Lisa Von Ahn)