Judge Garland will also confront the rise of domestic extremism as law enforcement officials continue investigating the Jan. 6 assault on the Capitol. His first briefings this week were expected to be with the F.B.I. director, Christopher A. Wray, to discuss the threat and with Michael R. Sherwin, the outgoing top prosecutor in Washington who has led the Justice Department inquiry.
The Capitol riot investigation has grown closer to Roger J. Stone Jr., one of Mr. Trump’s allies, and the F.B.I. has found evidence of communications between right-wing extremists and White House associates, underscoring how closely Mr. Trump had aligned himself with such groups during his presidency.
During his confirmation hearing, Judge Garland said that he would rely on his experience leading the department’s investigation into the Oklahoma City bombing to help again combat domestic extremism.
“I supervised the prosecution of the perpetrators of the bombing of the Oklahoma City Federal Building, who sought to spark a revolution that would topple the federal government,” he said. “I will supervise the prosecution of white supremacists and others who stormed the Capitol on January 6, a heinous attack that sought to disrupt a cornerstone of our democracy, the peaceful transfer of power to a newly elected government.”
During the Clinton administration, he was chosen by Jamie Gorelick, the deputy attorney general, to serve as her top deputy. He led the investigation into the 1995 Oklahoma City bombing, which led to the conviction and execution of Timothy McVeigh, and went on to supervise other high-profile cases that included the Unabomber, Theodore J. Kaczynski, and the bombing at the Atlanta Olympics in 1996.
The investigations helped cement Judge Garland’s reputation as a fair-minded centrist. After his appeals court confirmation, he did not make major headlines again until 2016, when Mr. Obama nominated him to serve on the Supreme Court, a choice that won bipartisan support, including from conservative stalwarts like the former Whitewater prosecutor Ken Starr.
But Mr. McConnell refused to consider his nomination, and Mr. Trump nominated Neil Gorsuch to fill the vacant seat in 2017. Judge Garland stayed on at the Court of Appeals.
Mr. McConnell, who said the last year that he would support Judge Garland to serve as attorney general, voted for Judge Garland’s confirmation on Wednesday and was one of 20 Republicans who voted a day earlier to end debate over his nomination and move it to a full vote of the Senate.