Home Secretary Priti Patel and Culture Secretary Nadine Dorries have said they will step down when Liz Truss becomes prime minister on Tuesday.
The BBC has been told Ms Dorries was asked to stay on but wants to return to writing books.
Ms Patel announced her decision in a letter to outgoing PM Boris Johnson in which said she would give Ms Truss her support from the backbenches.
The Witham MP said being home secretary had been “the honour of my life”.
Ms Truss had been expected to remove Ms Patel from the position when she begins announcing her new ministerial team.
Paragraph eq5iqo00″>However, Ms Patel – who has served as home secretary since 2019 – insisted leaving government was “her choice”.
She also said it was “vital” that Ms Truss backed “all aspects” of the policies she had put in place on illegal migration.
Writing to Mr Johnson, Ms Patel said: “Britain had always been a beacon for freedom and democracy and I have been proud to work with you over the last three years to make that light shine brighter.
All this has been achieved despite the relentless efforts of our political opponents and left-wing activists, lawyers and campaigners.”
At one stage this summer, Priti Patel considered a leadership bid of her own. At least a dozen colleagues pressed her to do so.
And some who would have supported her began to declare for other candidates. She – like the final two in the contest – was one of the most senior members of Boris Johnson’s government.
Insiders suggest she didn’t discern any abilities in them that she didn’t possess herself. So she endorsed neither of them – a potentially career-limiting move.
While she would have been happy to stay at the Home Office, the rumours that Suella Braverman would replace her were solidified by sources close to Liz Truss.
At that point, Priti Patel probably decided to jump before she was pushed – though she sent her resignation pointedly to the current Prime Minister, not his successor.
Thus the process of transition in government has begun.
And the speculation is whether Sunak supporter Dominic Raab may now follow suit.
In the role, she championed the controversial Online Safety Bill which aims to introduce rules about how platforms such as Facebook and Twitter should deal with harmful content.
Before joining the cabinet, Ms Dorries wrote a series of novels including the best-selling Four Streets based on her experience of growing up in Liverpool.
BBC politics editor Chris Mason said the Mid Bedfordshire MP had considered staying on as culture secretary but had decided to return to writing books.
Hours earlier, Ben Elliot resigned as Conservative co-chairman following Liz Truss’s election as party leader.
Mr Elliot oversaw a huge increase in donations to the party from wealthy individuals after his friend Boris Johnson gave him the role in 2019.
But he has also faced questions over his business interests and fundraising methods.
Last week, Labour urged Ms Truss and her then leadership rival Rishi Sunak to sack Mr Elliot if they became PM.
Announcing his resignation, Mr Elliot said it had been a “huge honour and privilege” to serve the Conservative Party.
“I would like to thank Boris Johnson for appointing me, and wish Liz Truss every success in leading our great country, particularly given the challenges of the winter ahead,” he added.
he wanted to give Ms Truss – who had earlier been announced the winner of the contest to succeed Mr Johnson as Tory leader and PM – the freedom to appoint her own party chair.
The nephew of Camilla, Duchess of Cornwall, Mr Elliot was educated at Eton and is known for being well-connected.
His company, Quintessentially, helps provide its wealthy clients with all the trappings of a luxury lifestyle – from yacht hire and holiday booking to private concerts with pop stars.
But last year, he was warned by a lobbying regulator to keep his private business interests and public role as Tory co-chairman separate.
The Office of the Registrar of Consultant Lobbyists (ORCL) had begun an investigation following reports suggesting Quintessentially had arranged access to top politicians for clients.
The watchdog found the company “had not been engaging in consultant lobbying activity” but said he should be “cautious” and ensure his two roles remain separate.
Mr Elliot’s spokesman said at the time: “The registrar has made clear that Quintessentially does not lobby government and therefore does not need to register as a lobbyist.”