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.