His pardon of Mr. Black, a personal friend and the author of pro-Trump opinion pieces as well as a flattering book, “Donald J. Trump: A President Like No Other,” is his first since the release of the special counsel’s report, which did not come to any conclusion on whether Mr. Trump obstructed justice. It comes as Mr. Trump has continued to vent publicly about being the target of what he views as an unjust “witch hunt.”

Mr. Black, who was born in Canada and is also known as Lord Black of Crossharbour, was charged with swindling his company, Hollinger International, of $60 million. He was sentenced to a prison term of six and a half years but was released after serving just over two years. After a federal judge ruled that Mr. Black had not served enough time, he returned for about a year.

In a statement, the White House press secretary, Sarah Huckabee Sanders, noted that the Supreme Court “largely disagreed” with the prosecutors who put Mr. Black in jail, and “overturned almost all charges in the case.” She added, “He nevertheless spent 3.5 years in prison.”

Ms. Sanders described Mr. Black, who once owned The Chicago Sun-Times, The Jerusalem Post and The Daily Telegraph in London, as “an entrepreneur and scholar” who “has made tremendous contributions to business, as well as to political and historical thought.” She also cited support for Mr. Black from Henry A. Kissinger, the former secretary of state; Rush Limbaugh, the conservative radio host and a frequent golf partner of the president’s; and the musician Elton John.

Mr. Black, an outsize character in the vein of the president, has a long history with him. During Mr. Black’s 2007 trial, Mr. Trump was expected to be called as a witness to bolster Mr. Black’s defense. He was expected to fly to Chicago and testify that a lavish $62,000 surprise party Mr. Black threw for his wife at the restaurant La Grenouille in New York — the bulk of which he charged to his company — was a business event, not a social event.