Edward O'Callaghan, a top U.S. Justice Department official in the Trump administration who played a lead role overseeing the Russia investigation, has joined the law firm Wilmer Cutler Pickering Hale and Dorr, a move that returns him to working alongside former Special Counsel Robert Mueller III.

Before stepping down in December, O'Callaghan served as the chief liaison between Mueller's team and the Justice Department leadership in his role as the top aide to then-Deputy Attorney General Rod Rosenstein. O'Callaghan, a former federal prosecutor in New York, initially headed the national security division when he returned to the Justice Department as a political appointee during the first year of the Trump presidency.

At Wilmer Hale, O'Callaghan will be a partner in the litigation and crisis management groups, specializing in white-collar defense and congressional investigations. His arrival comes six months after Mueller returned to the firm following his two-year tenure investigating Russia's interference in the 2016 election. Within the firm, O'Callaghan's hiring is seen as adding depth at a time when many in the legal industry anticipate increased congressional oversight and enforcement activity tied to the federal government's response to the coronavirus crisis.

O'Callaghan previously was a partner at the law firms Clifford Chance and Nixon Peabody. He joined the Trump administration from Clifford Chance, where he reported on a financial disclosure earning more than $2.24 million in 2017.

In an interview, O'Callaghan said he was drawn to Washington-based Wilmer Hale's "outstanding platform" for former senior government officials.

"Their record is kind of unmatched in terms of them being able to provide a platform and experience of folks in transitioning from government to private practice," he said. O'Callaghan noted that the firm's crisis management group is headed by former Deputy Attorney General Jamie Gorelick, who served as the second-ranking Justice Department official in the Clinton administration, and Robert Kimmitt, a former top Treasury Department official and ambassador to Germany.

"It just was a lot of folks I knew really well and whom I trusted. When you're going into a partnership, it makes the decision pretty easy," he said.

As the top aide to the Justice Department's second-ranking official, O'Callaghan advised Rosenstein and later Deputy Attorney General Jeff Rosen on policy matters and some of the federal government's most noteworthy investigations and cases.

In early 2019, during the frenzy that surrounded the delivery of the Mueller report to Justice Department leaders, O'Callaghan coordinated with federal prosecutors in Los Angeles and New York involved in the criminal case against Michael Avenatti, the California lawyer who ascended to fame representing Stephanie Clifford, the adult-film actress better known as Stormy Daniels, in lawsuits against Trump.

In a lesser-known case that resonated in Washington legal circles, O'Callaghan heard the last-ditch appeal from defense lawyers for Gregory Craig, the former White House counsel for President Barack Obama, who was later found not guilty in September of lying to the Justice Department about his work for Ukraine during his time as a partner at Skadden, Arps, Slate, Meagher & Flom.

As the acting assistant attorney general in charge of the Justice Department's national security division, O'Callaghan was involved in a U.S. government panel's recommendation to block Singapore-based Broadcom's hostile bid for rival chip maker Qualcomm. The panel, called the Committee on Foreign Investment in the United States, or CFIUS, cited Broadcom's connections to foreign entities in rejecting the acquisition on national security grounds.

O'Callaghan's tenure at Main Justice was highlighted by his role in the most consequential, and closely watched, investigation in recent memory.

O'Callaghan worked closely with Rosenstein, now a King & Spalding partner, in the oversight of the Russia investigation and played a direct role in the decision not to accuse Trump of obstruction of justice. He also advised Justice Department leaders, including U.S. Attorney General William Barr, on the release of the Mueller report in early 2019 and participated in the process of reviewing the more-than-400-page document to make it public with minimal redactions.

Barr's rollout of the special counsel's report was met with widespread consternation, as Mueller himself objected to the attorney general's early description of the findings as failing to "fully capture the context, nature, and substance of this office's work and conclusions." More recently, a federal judge in Washington lambasted Barr over the release of the report, writing in a decision last month that the attorney general's public statements appeared to spin the Mueller report's findings in favor of Trump.

O'Callaghan, in an interview, declined to discuss internal Justice Department deliberations but broadly defended the oversight of the special counsel investigation and handling of the Mueller report.

"I think that, at the end of the day, the people involved in it did their best to fairly describe what they thought were the most important, key factors in the report. And people can disagree about that, and they have. But I think everyone involved in it tried to be as fair as they could about it," he said.

Robert Mueller Robert Mueller, former special counsel for the U.S. Department of Justice, testifies before the House Judiciary Committee in Washington, D.C., on July 24, 2019. Credit: Diego M. Radzinschi / ALM

In the run-up to joining Wilmer Hale, O'Callaghan said he spoke with about 40 partners at the firm, including Aaron Zebley, who served as a top aide to Mueller during the special counsel investigation and appeared beside him during his testimony before the House. On a visit to the firm's Washington office, O'Callaghan said, he popped by Mueller's office to say hello to the former FBI director.

"Because I hold his opinion in such high regard, I certainly spoke with Aaron about his experience going back and what the transition was like. He had nothing but positive things to say about the firm embracing him and Bob," O'Callaghan said.

"Going forward, I'm thrilled to be able to work with them. Bob is one of the most highly regarded attorneys, certainly, that I had the good fortune of working with when he was [at the] FBI and through the special counsel process."

O'Callaghan dismissed the notion that his oversight of the Russia investigation, including the apparent rift over the Mueller report's release last year, would create a complicated working relationship.

"I expect to be working with [Mueller] and Aaron Zebley," he said, "and feel very comfortable with that."