The Republican says the vote was “personal”, lashing out at his political nemesis, Matt Gaetz.
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Kevin McCarthy has been ousted in a right-wing revolt – the first time ever that a US House of Representatives’ Speaker has lost a no-confidence vote.
The final tally was 216-210 to remove the California congressman as leader of the Republican majority in the lower chamber of Congress.
Ultra-conservatives mutinied after he struck a deal on Saturday with Senate Democrats to fund government agencies.
There is no obvious successor to oversee the House Republican majority.
Florida Republican Matt Gaetz, a Trump ally, filed the procedural tool on Monday night to oust Mr McCarthy.
He accused the Speaker of making a secret deal with the White House to continue funding for Ukraine.
At a private meeting of Republican lawmakers on Tuesday evening, Mr McCarthy told his colleagues he does not plan to run for Speaker again.
He later took aim at his political nemesis, Mr Gaetz, accusing him of attention-seeking.
“You know it was personal,” Mr McCarthy told a news conference, “it had nothing to do with spending.”
He said fundraising emails sent by Mr Gaetz amid the infighting were “not becoming of a member of Congress”.
The hardliners who ousted him “are not conservatives”, Mr McCarthy added.
He only became Speaker in January after a gruelling 15 rounds of voting in the chamber as Mr Gaetz and other right-wingers refused to support him.
Eight Republicans voted to oust Mr McCarthy in Tuesday’s vote. Another 210 – all Republicans – voted to keep Mr McCarthy in the role.
But Democrats joined with the Speaker’s Republican critics to topple him.
Democratic House Leader Hakeem Jeffries had said in a letter to colleagues that he would not provide the votes needed to rescue Mr McCarthy.
Congresswoman Pramila Jayapal, a left-wing Democrat from the north-western US state of Washington, told reporters before the vote: “Let them wallow in their pigsty of incompetence.”
After the vote, two Democratic lawmakers laughed about the Republican feuding.
“Let the civil war begin,” one of them quipped in a lift.
The packed chamber – which Republicans control by a narrow 221-212 majority – was mostly silent as members awaited the result of the roll call vote.
“The office of Speaker of the House is hereby declared vacant,” declared Arkansas Republican Steve Womack with a bang of his gavel, to audible gasps.
Ahead of the vote former US President Donald Trump posted on his social media platform, Truth Social, that the party should be “fighting the Radical Left Democrats” instead of each other.
During Tuesday’s debate, all of the next three top-ranking members rose to speak in Mr McCarthy’s defence.
House Republican Conference chairwoman Elise Stefanik praised Mr McCarthy as “a happy warrior”.
One vote against Mr McCarthy that surprised many observers came from a moderate Republican, Nancy Mace.
The South Carolina lawmaker said after the vote: “I am looking for a Speaker who will tell the truth to the American people. Who will be honest and trustworthy with Congress, with both parties.”
After ousting Mr McCarthy, Mr Gaetz sounded unconcerned when asked whether his colleagues might attempt to remove him.
He told reporters outside the Capitol: “If they want to expel me let me know when they have the votes.”
North Carolina Republican Patrick McHenry, who supported Mr McCarthy, is now the Speaker pro tempore, or interim Speaker. He gavelled the House into recess.
It is unclear if the temporary Speaker will have the full powers of the office, or merely administrative powers and the ability to supervise a new election.
The rules do not state how long a person could fill in as an interim Speaker or when a new election would be held.
It is not clear who will replace Mr McCarthy, but Louisiana Republican Steve Scalise and Minnesota Republican Tom Emmer have been mentioned as contenders – though they have not expressed any interest in the role.
White House press secretary Karine Jean-Pierre said in a statement that President Joe Biden “hopes the House will quickly elect a Speaker”, noting that the “challenges facing our nation will not wait”.
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The Speaker is second in the line of succession for the presidency after the US vice-president. He or she sets the lower house of Congress’s legislative priorities, controls committee assignments, and can make or break the White House’s agenda.
The last two Republican Speakers – Paul Ryan and John Boehner – left Congress after repeated tangles with their more conservative colleagues.
The so-called motion to vacate had only previously been used twice in the past century to remove a Speaker – in 2015 and 2010 – though never successfully until Tuesday.
(With additional reporting from Kayla Epstein and Max Matza)