Kevin McCarthy has been toppled 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 congressman as leader of the Republican majority in the lower chamber of Congress.
Hardliners in his party voted against him after he struck a deal with Senate Democrats to fund government agencies.
There is no clear successor to oversee the House Republican majority.
Congress has just over 40 days to agree on a deal to avoid another potential government shutdown.
Florida Republican Matt Gaetz, a Trump ally, filed a rarely used procedural tool known as a motion to vacate 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, amid negotiations to avert a partial government shutdown at the weekend. Mr McCarthy denies it.
At a private meeting of Republican politicians on Tuesday evening after losing his job, Mr McCarthy told colleagues he did not plan to run for Speaker again.
He later took aim at his political nemesis, Mr Gaetz, accusing him of attention-seeking.
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.
To win over those hardliners Mr McCarthy agreed to make it possible for a single member to put forward a motion to oust him, which is exactly what Mr Gaetz ultimately did.
Mr McCarthy was supported by 210 Republicans but eight voted against him in Tuesday’s vote, joining all Democrat members.
They were Mr Gaetz, Eli Crane, Andy Biggs, Ken Buck, Tim Burchett, Bob Good, Matt Rosendale and Nancy Mace.
One vote against Mr McCarthy that surprised many came from Ms Mace – a moderate Republican from South Carolina.
She said afterwards: “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.”
Democratic House Leader Hakeem Jeffries had said in a letter to colleagues that he would not provide the votes needed to rescue Mr McCarthy.