Priti Patel has said she is quitting as Home Secretary and will not serve in Liz Truss' Cabinet.
The top Tory said it was "my choice to continue my public service to the country and to the Witham constituency from the backbenches" as she jumped before she was pushed.
She was widely expected to get the sack when Ms Truss reshuffles her Cabinet - with hard-line Attorney General Suella Braverman tipped to be the next Home Secretary.
But Ms Patel tried to suggest that she was choosing to step down rather than being forced out by the new PM.
"I congratulate Liz Truss on being elected our new leader, and will give her my support as our new Prime Minister," her letter to Boris Johnson said.
"It is my choice to continue my public service to the country and the Witham constituency from the backbenches, once Liz formally assumes office and a new Home Secretary is appointed."
Ms Patel has been Home Secretary since Boris Johnson became Tory leader in July 2019 and was International Development Secretary under Theresa May before she was sacked for holding unauthorised meetings with Israeli officials in 2017.
She has been a divisive figure at the Home Office, presiding over the controversial Rwanda deportation scheme as she struggled to tackle the rising numbers of asylum seekers arriving in Britain in small boats.
Ms Patel sought to blame "activist lawyers" for the Government's failure to get the scheme off the ground
Mr Johnson stuck by her when his ethics chief found she had shouted and swore at her officials in actions "that can be described as bullying".
Sir Alex Allan, the PM's adviser on Ministerial Standards, found in November 2020 that she broke the Ministerial Code with her conduct - "even if unintentionally".
But the PM said he would "stick with Prit" and kept her in post. Sir Alex then resigned.
Her announcement comes as ministers brace for a clear-out at the top of Government, after Ms Truss won the Tory leadership race today with 57% of the vote.
Cabinet Office Minister Nigel Adams, a close Johnson ally, also said he was intending to stand down, as well as Conservative Party co-chairman Ben Elliot.
Ms Truss will formally take over as Prime Minister on Tuesday after a private audience with the Queen at Balmoral.
One of her first tasks will be to reshuffle her Cabinet, with top jobs expected for right-wingers and close allies.
Business Secretary Kwasi Kwarteng is tipped to be Chancellor, with Education Secretary James Cleverly as Foreign Secretary and Suella Braverman, the Attorney General, heading up the Home Office.
