Securities and Exchange Commission Chairman Mary Schapiro, who took the agency's helm in 2009 as it reeled from public rebukes for failing to rein in Wall Street practices that exacerbated losses from the housing market collapse, is leaving the agency next month.

Schapiro, 57, will depart the SEC on Dec. 14, the agency said in a statement.

Elisse Walter, an SEC commissioner and former senior executive vice president at the Financial Industry Regulatory Authority, will serve as chairman after Schapiro steps down, the White House said in a statement.

"It has been an incredibly rewarding experience to work with so many dedicated SEC staff who strive every day to protect investors and ensure our markets operate with integrity," Schapiro said in the statement. "We have brought a record number of enforcement actions, engaged in one of the busiest rulemaking periods, and gained greater authority from Congress to better fulfill our mission."

Schapiro's departure comes as the agency navigates through a flood of new mandates generated by the Dodd-Frank Act and a wave of enforcement matters stemming from the financial market turmoil of 2008.

The former chairman and chief executive officer of Finra and chairman of the Commodity Futures Trading Commission was appointed by President Barack Obama to run the SEC in January of 2009. A political independent, she replaced Christopher Cox, a Republican who had held the office since 2005, becoming the first woman to lead the commission on a permanent basis.

"When Mary agreed to serve nearly four years ago, she was fully aware of the difficulties facing the SEC and our economy as a whole," Obama said in a statement. "But she accepted the challenge, and today, the SEC is stronger and our financial system is safer and better able to serve the American people – thanks in large part to Mary's hard work."

The start of Schapiro's tenure was dominated by public criticism over the agency's failure to detect Bernard L. Madoff's multi-billion dollar fraud, which was uncovered just a month before her appointment. At the same time, the regulator was under fire for its role in supervising Lehman Brothers Holdings Inc., which filed the biggest U.S. bankruptcy in September 2008, sending financial markets into a tailspin.

Schapiro later tapped Robert Khuzami, a former federal prosecutor, to reinvigorate the agency's enforcement division, setting in motion the biggest overhaul in that unit's history. The enforcement division, which has since filed dozens of cases related to the financial crisis, has also faced criticism from lawmakers, judges and investors that it has gone easy on top executives.

In the most prominent enforcement effort after the 2008 financial crisis, Schapiro's SEC sued Goldman Sachs Group Inc. in 2010, accusing it of fraud when it sold investors a mortgage security without disclosing that hedge fund Paulson & Co. helped pick the loans and bet against them. Goldman paid a record $550 million fine.

Schapiro's SEC has struggled to show it has a grasp on an increasingly fragmented market dominated by electronic and high- speed trading. She has supervised adjustments of trading practices and set the stage for a future computer surveillance system after a computer program employed by one firm sparked a 20-minute plunge in stock prices, temporarily erasing $862 billion of market value.

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