The Kentucky lawmaker, whose skills as a political power broker led to a 6-3 conservative majority on the Supreme Court, announced his retirement from the Senate on his 83rd birthday, describing his experience in the chamber since 1985 as "the honour of a lifetime".
In recent years, McConnell has seen the Republican Party move away from his traditional conservative style of politics towards the populist pugilism of President Donald Trump, a figure who McConnell blamed for the January 6, 2021, US Capitol riot, though he also voted to acquit him in the impeachment trial that followed and supported his re-election bid in 2024.
"The only appropriate thing to take away today, apart from a healthy dose of pride, is my immense gratitude for the opportunity to take part in the consequential business of the Senate and the nation," McConnell said in a floor speech on Thursday.
An unabashed defence hawk, McConnell expressed concern that the political commitment to American military power has waned since he entered the Senate during Ronald Reagan's presidency.
"The work of strengthening America's hard power was well under way when I arrived in the Senate. But since then, we've allowed that power to atrophy. And today, a dangerous world threatens to outpace the work of rebuilding it," he said.
In recent months, McConnell's tenure has been punctuated by physical ailments including injuries from falls and occasions during which he froze up in the midst of public remarks.
Two weeks ago, he fell down a set of stairs in the Capitol and later had to travel the halls of Congress by wheelchair.
His retirement will give Kentucky an open Senate seat in the 2026 election.
Before his replacement as Senate Republican leader by John Thune in 2024, McConnell gleefully accepted the nickname "Grim Reaper" for his readiness to use the levers of power to kill off Democratic initiatives in the Senate.
He is also proud of his decision in 2016 to prevent former president Barack Obama naming Merrick Garland to the Supreme Court seat vacated by the death of conservative Antonin Scalia.
That move allowed Trump later to cement a conservative court majority, paving the way for landmark rulings that ended the recognition of a constitutional right to abortion and expanded gun rights.
While critics accuse Republican lawmakers of serving as a rubber stamp for Trump's demands, McConnell said on Thursday that he would devote his remaining time to defending the integrity of the Senate and its guarantee of leverage for political minorities.
"The Senate is still equipped for work of great consequence. And to the disappointment of my critics, I'm still here on the job," McConnell said.
