McConnell, the longest-serving Senate party leader in US history, chose his 83rd birthday to share his decision not to run for another term in Kentucky and to retire when his current term ends. He informed The Associated Press of his decision before he was set to address colleagues in a speech on the Senate floor on Thursday (Friday AEDT).

His announcement begins the epilogue of a storied career as a master strategist, one in which he helped forge a conservative Supreme Court and steered the Senate through tax cuts, presidential impeachment trials and fierce political fights.

“Seven times, my fellow Kentuckians have sent me to the Senate,” McConnell said in prepared remarks provided in advance to the AP.

“Every day in between I’ve been humbled by the trust they’ve placed in me to do their business here. Representing our commonwealth has been the honour of a lifetime.

“I will not seek this honour an eighth time. My current term in the Senate will be my last.”

McConnell, first elected in 1984, intends to serve the remainder of his term ending in January 2027. The Kentuckian has dealt with a series of medical episodes in recent years, including injuries sustained from falls and times when his face briefly froze while he was speaking.

The senator plans to deliver his speech in a chamber the famously taciturn McConnell revered as a young intern long before joining its back benches as a freshman lawmaker in the mid-1980s.

McConnell’s looming departure reflects the changing dynamics of the Trump-led GOP. He’s seen his power diminish on a parallel track with both his health and his relationship with Trump, who once praised him as an ally but has taken to criticising him in caustic terms.

In Kentucky, McConnell’s departure will mark the loss of a powerful advocate and will set off a competitive GOP primary next year for what will now be an open Senate seat. Kentucky Democratic Governor Andy Beshear, seen as a rising star in his party for winning statewide office in Republican territory, has said he has no interest in the Senate, though he is widely viewed as a contender for higher office.

McConnell, a diehard adherent to Ronald Reagan’s brand of traditional conservatism and muscular foreign policy, increasingly found himself out of step with a GOP shifting toward the fiery, often isolationist populism espoused by Trump.

McConnell still champions providing Ukraine with weapons and other aid to fend off Russia’s invasion, even as Trump ratchets up criticism of the country and its leader, Volodymyr Zelenskyy. The senator plans to make it clear Thursday that national defense remains at the forefront of his agenda.

“Thanks to Ronald Reagan’s determination, the work of strengthening American hard power was well underway when I arrived in the Senate,” McConnell said in his prepared remarks.

“But since then, we’ve allowed that power to atrophy. And today, a dangerous world threatens to outpace the work of rebuilding it.

“So, lest any of our colleagues still doubt my intentions for the remainder of my term: I have some unfinished business to attend to.”

McConnell and Trump were partners during Trump’s first term, but the relationship was severed after McConnell blamed Trump for “disgraceful” acts in the January 6, 2021, Capitol attack by his supporters. A momentary thaw in 2024 when McConnell endorsed Trump didn’t last.

Last week, Trump referred to McConnell as a “very bitter guy” after McConnell, who battled polio as a child, opposed vaccine sceptic Robert F Kennedy Jr’s confirmation as the nation’s top health official.

McConnell referred to Trump as a “despicable human being” and a “narcissist” in a biography of the senator by The Associated Press’ deputy Washington bureau chief, Michael Tackett.