WASHINGTON — Robert S. Mueller III rejoined the law firm WilmerHale on Tuesday, just months after retiring as special counsel in the investigation into Russia’s election interference and President Trump’s efforts to impede it.
Mr. Mueller returned to the Washington office of the firm, known for housing former high-level government officials. He worked as a partner there after he departed as F.B.I. director in 2013 and until he was tapped to oversee the Russia investigation in 2017. He is expected to resume work conducting internal investigations for large corporations.
“We expect that will be the focus of his practice now that he’s back,” said Robert T. Novick, a WilmerHale managing partner. He said Mr. Mueller’s work could include assessing how organizations function and whether they are prepared for potential crises.
Two of Mr. Mueller’s deputies in the Russia investigation, James L. Quarles III and Aaron M. Zebley, also worked as partners at WilmerHale before joining the special counsel’s office and have returned, as well. The three used a WilmerHale annex to prepare for Mr. Mueller’s high-profile congressional testimony in July.
Mr. Mueller and Mr. Zebley, who was also his chief of staff at the F.B.I., will most likely work together on some projects, as they did before the Russia investigation.
“They hadn’t thought about a return until they were done,” said William F. Lee, a partner in the firm’s Boston office who has known Mr. Mueller and Mr. Quarles for decades. “That’s just the nature of who they are.”
Mr. Mueller made clear that he sought flexibility to speak publicly and teach, according to a person familiar with the negotiations.
During a foray into private practice in the mid-1990s at a firm that later became WilmerHale in a merger, Mr. Mueller found that it tested his views honed over decades in law enforcement. When he received a corporate-malfeasance case, he reportedly told a colleague that the defendant was “right where he belongs” — in jail.
Mr. Mueller surprised even his closest associates by returning to government in 1995 as a homicide prosecutor in Washington, where he traveled to grisly crime scenes and examined bullet casings.
He rose up the Justice Department ranks for a second time and ascended to F.B.I. director for a 12-year stint, the longest since J. Edgar Hoover, before joining WilmerHale in 2013. He earned an annual salary in the millions of dollars working for organizations like the N.F.L., for which he compiled an almost 100-page report detailing the league’s response to the Ray Rice domestic violence scandal.
Several other special counsel prosecutors have joined private law firms since their inquiry concluded. Jeannie Rhee, who led the Russia component of the investigation, joined the firm Paul, Weiss. Andrew D. Goldstein, who oversaw the investigation into whether Mr. Trump obstructed justice, began working for the firm Cooley. Greg D. Andres, the lead prosecutor in the trial of Paul Manafort, returned to the firm Davis Polk & Wardwell. And Zainab Ahmad, who prosecuted Michael T. Flynn, Mr. Trump’s former national security adviser, joined Gibson, Dunn & Crutcher.
On his first day back, Mr. Mueller had a somewhat simpler puzzle than determining whether a presidential campaign engaged in a sprawling criminal conspiracy with a foreign power.
“He’s just being refreshed on how to use the computers,” Mr. Novick said. “If he’s doing any more than that, I’d be really impressed. I doubt it’s a highly revenue-generating day.”