President Trump pardoned former Maricopa County Sheriff Joe Arpaio of Arizona Friday night, saying the 85-year-old figure in the national debate over immigration is “a worthy candidate for a presidential pardon.”

The White House said Mr. Arpaio was engaged for more than a half century in his “life’s work of protecting the public from the scourges of crime and illegal immigration.” “After more than fifty years of admirable service to our nation, he is worthy candidate for a presidential pardon,” the White House said.

The president had been broadly hinting that he might issue a pardon for Mr. Arpaio, who was convicted by a judge last year of criminal contempt for ignoring order last year to stop detaining people he suspected of being undocumented immigrants.

“So was Sheriff Joe convicted of doing his job?” Mr. Trump said at a rally in Phoenix Tuesday night to loud cheers. “You know what, I’ll make a prediction: I think he’s going to be just fine, okay? But I won’t do it tonight because I don’t want to cause any controversy. But Sheriff Joe should feel good.”

Mr. Arpaio lost a bid for re-election last November.

The White House said Mr. Arpaio’s life and career, which began at the age of 18 when he enlisted in the military after the outbreak of the Korean War, “exemplify selfless public service.”

After serving in the Army, Mr. Arpaio became a police officer in Washington, D.C. and Las Vegas, Nevada, and later served as an agent for the Drug Enforcement Administration.