Mitch McConnell, the longest-serving US Senate leader in history, who maintained his power in the face of dramatic convulsions in the Republican Party for almost two decades, will step down in November.

Mr McConnell, who turned 82 last week, announced his decision on Wednesday in the well of the Senate, a place where he looked in awe from its back benches in 1985 when he arrived and where he grew increasingly comfortable in the front row seat afforded the party leaders.

“One of life’s most underappreciated talents is to know when it’s time to move on to life’s next chapter,” he said. “So I stand before you today to say that this will be my last term as Republican leader of the Senate.”

His decision punctuates a powerful ideological transition under way in the Republican Party, from Ronald Reagan’s brand of traditional conservatism and strong international alliances, to the fiery, often isolationist populism of former president Donald Trump.

McConnell said he plans to serve out his Senate term, which ends in January 2027, “albeit from a different seat in the chamber”.

Aides said Mr McConnell’s announcement was unrelated to his health. The Kentucky senator had concussion from a fall last year and two public episodes where his face briefly froze while he was speaking.

“As I have been thinking about when I would deliver some news to the Senate, I always imagined a moment when I had total clarity and peace about the sunset of my work,” McConnell said.

“A moment when I am certain I have helped preserve the ideals I so strongly believe. It arrived today.”

The senator had been under increasing pressure from the restive, and at times hostile wing of his party that has aligned firmly with Mr Trump.

The two have been estranged since December 2020, when Mr McConnell refused to abide by Mr Trump’s lie that the election of Democrat Joe Biden as president was the product of fraud.

But while Mr McConnell’s critics within the Republican party conference had grown louder, their numbers had not grown appreciably larger, a marker of his strategic and tactical skill and his ability to understand the needs of his fellow Republican senators.

Mr McConnell gave no specific reason for the timing of his decision, which he has been contemplating for months, but he cited the recent death of his wife’s youngest sister as a moment that prompted introspection.

Senate McConnell
Mitch McConnell after delivering remarks on the Senate floor (Mark Schiefelbein/AP)

“The end of my contributions are closer than I’d prefer,” Mr McConnell said.

But his remarks were also light at times as he talked about the arc of his Senate career.

He noted that when he arrived in the Senate, “I was just happy if anybody remembered my name.”

During his campaign in 1984, when Mr Reagan was visiting Kentucky, the president called him “Mitch O’Donnell”.

Mr McConnell endorsed Mr Reagan’s view of America’s role in the world and the senator has persisted in face of opposition, including from Mr Trump, that Congress should include a foreign assistance package that includes 60 billion dollars (£47 billion) for Ukraine.

“I am unconflicted about the good within our country and the irreplaceable role we play as the leader of the free world,” Mr McConnell said.

Against long odds he managed to secure 22 Republican votes for the package now being considered by the House.

“Believe me, I know the politics within my party at this particular moment in time. I have many faults. Misunderstanding politics is not one of them,” Mr McConnell said.

“That said, I believe more strongly than ever that America’s global leadership is essential to preserving the shining city on a hill that Ronald Reagan discussed.

“For as long as I am drawing breath on this earth I will defend American exceptionalism.”