Ten Republican House members, including the No.3 House GOP leader, have voted to impeach President Donald Trump over the deadly insurrection at the Capitol.
The votes were in sharp contrast with the unanimous support for Trump among House Republicans when he was impeached by Democrats in December 2019.
Cheney, whose decision to buck Trump sparked an immediate backlash within the GOP, was the only member of her party's leadership to support impeachment, which was opposed by 197 Republicans.
"There has never been a greater betrayal by a president of the United States of his office and his oath to the Constitution," said Cheney, whose father, Dick Cheney, served as vice-president under George W Bush.
The younger Cheney has been more critical of Trump than other GOP leaders but her announcement hours before Wednesday's vote nonetheless shook Congress.
Trump "summoned" the mob that attacked the Capitol, "assembled the mob, and lit the flame of this attack," Cheney said, adding: "Everything that followed was his doing."
Trump could have immediately intervened to stop his supporters from rioting but did not, she said.
Cheny had not qualms about her vote. "I'm not going anywhere," the three-term congresswoman proclaimed to reporters after some back-bench Republicans angrily demanded she be fired from her leadership position.
Nine other House Republicans also supported impeachment: John Katko of New York; Adam Kinzinger of Illinois; Anthony Gonzalez of Ohio; Fred Upton and Peter Meijer of Michigan; Jaime Herrera Beutler and Dan Newhouse of Washington state; Tom Rice of South Carolina; and David Valadao of California.
Trump's fate is now up the Republican-controlled Senate, which acquitted him last year without hearing witnesses in a trial. This time, however, Senate Majority Leader Mitch McConnell is angry at Trump, not only over the Capitol insurrection but also the twin defeats in Georgia the day before that cost the GOP its Senate majority, according to a Republican granted anonymity to discuss the situation.
McConnell said he had not made a final decision on how he would vote and would listen to legal arguments presented in a Senate trial, which will not be concluded before Biden's January 20 inauguration.
At least two GOP senators - Lisa Murkowski and Pat Toomey - have said they support impeachment or have called on Trump to resign. Senator Ben Sasse, has said he will consider impeachment.
Only one Republican senator, Mitt Romney, voted to convict Trump last year.