President Biden issued a full and unconditional pardon of his son Hunter on Sunday night after repeatedly insisting he would not do so, using the power of his office to wave aside years of legal troubles, including a federal conviction for illegally buying a gun and for tax evasion.

In a statement issued by the White House, Mr. Biden said he had decided to issue the executive grant of clemency for his son “for those offenses against the United States which he has committed or may have committed or taken part in during the period from Jan. 1, 2014, through Dec. 1, 2024.”

He said he made the decision because the charges against Hunter were politically motivated and designed to hurt him politically.

“The charges in his cases came about only after several of my political opponents in Congress instigated them to attack me and oppose my election,” Mr. Biden said in the statement. “No reasonable person who looks at the facts of Hunter’s cases can reach any other conclusion than Hunter was singled out only because he is my son — and that is wrong.”

He added: “There has been an effort to break Hunter — who has been five and a half years sober, even in the face of unrelenting attacks and selective prosecution. In trying to break Hunter, they’ve tried to break me — and there’s no reason to believe it will stop here. Enough is enough.”

It was a remarkable turnaround for a man whose presidency and five-decade career was built in part on the idea that he would never interfere with the administration of justice. In 2020, he made the case that former President Donald J. Trump should be ousted from office to restore that kind of independence in America’s democracy, and he argued the same in 2024.

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