U.S. Deputy Solicitor General Michael Dreeben leaves the U.S. Justice Department on his way to argue his one-hundredth case before the U.S. Supreme Court in Washington on April 27, 2016. (Jonathan Ernst/REUTERS)

Michael R. Dreeben, who represented the federal government in 105 cases before the Supreme Court and most recently was part of special counsel Robert S. Mueller III’s investigation team, is ending his career at the Justice Department.

Dreeben served as deputy solicitor general and was responsible for the criminal docket in the office that represents the government in the courts of appeals and the Supreme Court. He is widely respected for his expertise in the field and trusted by Supreme Court justices, whom he has worked with and opposed in court.

Dreeben made his first argument before the court in 1989, and the lawyer on the other side was John G. Roberts Jr., now the chief justice. (Roberts won the case.)

In 2016, after Dreeben made his 100th argument at the high court, Roberts noted the occasion from the bench.

“You are the second person to reach that rare milestone this century,” the chief justice said. “I distinctly recall your first argument. . . . You have consistently advocated positions on behalf of the United States in an exemplary manner.”

Dreeben on Wednesday declined to comment on his next move.

Solicitor General Noel J. Francisco issued a statement: “On behalf of the Office of the Solicitor General, I thank Michael for his many years of service to the Department. We wish him the best of luck in the next chapter of his career.”

While the solicitor general and the No. 2 person in the office are political appointees, others are career lawyers who serve one administration after another. Justice Elena Kagan, for instance, has said she depended on Dreeben and Deputy Solicitor General Edwin Kneedler when President Barack Obama nominated her to be solicitor general.

Many of the top Supreme Court practitioners served in what lawyers call “the SG’s office,” and they offered tributes to Dreeben.

“A first-ballot Hall of Famer in the Supreme Court bar,” tweeted Washington lawyer Kannon Shanmugam.

Dreeben took a sabbatical from the office to work for Mueller and filled a critical role in fending off challenges to the special counsel’s authority. When former Trump campaign chairman Paul Manafort argued that Mueller should not be allowed to investigate his business dealings in Ukraine, Dreeben was the lawyer who argued in court that the special counsel was operating well within his scope.

Dreeben similarly argued against a challenge from Andrew Miller, an associate of President Trump’s longtime friend Roger Stone who said that Mueller’s appointment was unconstitutional because of the manner in which he was named to his post.

Matt Zapotosky contributed to this report.