The Justice Department’s Assistant Attorney General for the Criminal Division Lanny A. Breuer addresses the media while announcing new criminal charges against oil company BP on Nov. 15. Breuer is leaving the department after leading the agency’s efforts to clamp down on public corruption and financial fraud. (Sean Gardner/GETTY IMAGES)

Lanny A. Breuer is leaving the Justice Department after leading the agency’s efforts to clamp down on public corruption and financial fraud at the nation’s largest banks, according to several people familiar with the matter.

As one of the longest-serving heads of the criminal division, Breuer has had a tenure filled with controversy and high-profile prosecutions. He was admonished for his role in the agency’s botched attempt to infiltrate weapons-smuggling rings in the operation dubbed “Fast and Furious.” And he has been accused of being soft on Wall Street for failing to throw senior bank executives behind bars for their role in the financial crisis.

Yet Breuer is widely credited with aggressively going after white-collar crime in the aftermath of the crisis. He also stepped up the division’s involvement in money-laundering cases, launching a series of criminal investigations that have resulted in multimillion-dollar settlements.

It is not clear when Breuer intends to leave his post, nor what he plans to do once he departs, but it is certain that the prosecutor’s days in office are winding down, according to people who were not authorized to speak publicly about the matter.

Officials at the Justice Department, including Breuer, declined to comment for this article.

When Breuer was confirmed as assistant attorney general for the criminal division in April 2009, the agency was tainted by allegations of political interference in prosecutions and unprofessional conduct during the George W. Bush administration. The department continues to be mired in controversy stemming from the Bush years.

During Senate hearings in 2011, Breuer conceded that he had failed to alert other Justice Department officials that federal agents had allowed guns to illegally flow into Mexico and onto U.S. streets between 2006 and 2007. The practice, known as “gun walking,” was also a key part of the Obama administration’s Phoenix gun-tracking operation, “Fast and Furious.”

The operation came under fire when many of the weapons later turned up at crime scenes in Mexico and the United States, including two where a Border Patrol agent was killed.

Several officials at the Justice Department resigned in connection with the operation, including Jason Weinstein, a deputy assistant attorney general in the criminal division. Breuer later apologized for his inaction when the tactics first came to his attention. Sen. Charles E. Grassley (R-Iowa) called for his resignation, but Attorney General Eric H. Holder Jr. stood behind Breuer.

A former prosecutor in the Manhattan district attorney’s office, Breuer came to the Justice Department well versed in white-collar crime. He has been a driving force behind the prosecution of banks involved in rigging the global interest rate known as Libor. His efforts helped produce a $1.5 billion settlement with UBS and led to criminal indictments against two of the bank’s former traders in December.

But Breuer and his team were blasted for not indicting the parent company and more of its executives given the broad scope of problems at UBS.

Critics have also decried Breuer’s routine use of deferred prosecution, which gives the agency the right to go after a company in the future if it fails to comply with the terms of the agreement. They say the use of such tactics amounts to a slap on the wrists of companies that have engaged in egregious behavior. Breuer, however, has argued that the agreements result in greater accountability for corporate wrongdoing.

Breuer made a name for himself as special counsel to President Bill Clinton, whom he represented in the 1998 impeachment hearings and the Whitewater investigation.

Before his appointment at the Justice Department, Breuer had worked at the Washington office of the Covington & Burling law firm, alongside Holder. While there, Breuer defended former Clinton national security adviser Samuel R. “Sandy” Berger, who was being investigated for tampering with presidential documents at the National Archives. He also represented baseball pitcher Roger Clemens in proceedings before the House Committee on Oversight and Government Reform about the use of steroids.