(Image Credit: Evan Vucci/AP Photo)

The head of the government's financial sector watchdog is stepping down.

Mary Schapiro, who chairs the Securities and Exchange Commission, announced today that she will leave her post next month after four years of working to retool the agency after a severe financial crisis it failed to prevent.

"Over the past four years, we have brought a record number of enforcement actions, engaged in one of the busiest rule-making periods, and gained greater authority from Congress to better fulfill our mission," Schapiro said in a statement.

Appointed by President Obama in January 2009 and unanimously confirmed, Schapiro was the first woman to lead the SEC.

"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 administration has praised Schapiro, 57, for mounting more aggressive enforcement operations across the financial industry, initiating a record number of cases, and for helping shape the new set of regulations and consumer protections included in the Dodd-Frank Wall Street overhaul legislation.

But critics point out that Schapiro's SEC failed to nab and punish financial industry wrongdoers in any significant way, although some would likely agree that she has improved the agency from where it was in 2008, when, among the agency's many failures, it missed the Bernie Madoff Ponzi scheme.

Obama has named SEC commissioner Elisse Walter - a George W. Bush appointee - to chair the agency going forward.

ABC News' Zunaira Zaki contributed.