Nadine Dorries has confirmed she was asked by Liz Truss to stay on as Culture Secretary but chose instead to return to the backbenches when the new PM takes the reins.
The Tory MP – who was a loyal ally to Boris Johnson during his tenure and backed Ms Truss for leader – said she has decided to leave the Cabinet “after much reflection”.
She said she will be “better placed” to support the new PM from outside the top team.
It is expected that she will now be given a peerage in Mr Johnson’s resignation honours list, triggering a by-election in her Mid Bedfordshire constituency.
“I know that Liz will be a worthy successor; protecting your legacy and providing both leadership and vision for the nation,” she said.
“I am humbled that your successor has extended her confidence in me by asking me to remain as Secretary of State for DCMS.
“However, after much reflection, I am writing to you to resign as Secretary of State for Digital, Culture, Media and Sport at the point at which your successor is appointed.
“I have personally assured our soon-to-be prime minister that I will be better placed to support her from outside of the Cabinet.”
During the leadership campaign, Ms Dorries was an outspoken critic of Rishi Sunak – in one controversial tweet likening him to Brutus stabbing Julius Caesar over the way he had turned on Mr Johnson.
She accused fellow Tory MPs of staging a “coup” against the outgoing PM, telling BBC Panorama: “I was quite stunned that there were people who thought that removing the Prime Minister who won the biggest majority that we’ve had since Margaret Thatcher in less than three years.
“Just the anti-democratic nature of what they’re doing alone was enough to alarm me. And for me it was a coup.”
She was also among Mr Johnson’s most outspoken defenders during the ‘partygate’ saga, calling an investigation by the Commons Privileges Committee into whether he lied to MPs a “witch hunt”, adding it represented the “most egregious abuse of power”.
Ms Dorries was appointed Culture Secretary in September last year, having previously served as health minister.
She was involved in drawing up legislation to curb social media companies through the Online Safety Bill and led controversial moves to privatise Channel 4.
In her letter to Mr Johnson, she said: “When I arrived in the department the Online Safety Bill had been kicked into the long grass.
“We picked it up, we ran with it and I am proud that we have a Bill which will hold tech giants to account and protect the lives of millions of children and young people.
“The eyes of the world are on this Bill and we, the UK, are leading the way.”
Ms Dorries stunned a rugby league audience in St Helens by referring to Jonny Wilkinson’s match-winning drop goal for England in the 2003 Rugby Union World Cup final in Sydney.
She later said this helped boost attention for the sport, telling MPs “rugby league has never had so much publicity and so much attention for the game”.
Ms Dorries was born in 1957 in Liverpool and grew up on a council estate, which she writes about on her official website, saying: “I am one of the luckiest people alive, to have grown up on a Liverpool council estate from the 1950s to 1970s.”
Her career as a writer has seen her author more than 10 books, among them The Four Streets Quartet novels, as well as The Angels series about the nurses of Lovely Lane. Her collection also includes The Tarabeg Trilogy.
Before being elected to Parliament as MP for Mid Bedfordshire in 2005, she worked for three years as an adviser to the former shadow home secretary and shadow chancellor Oliver Letwin.
Ms Dorries was thrust into the limelight in 2012 when she was suspended from the Conservative Party for appearing on ITV’s I’m a Celebrity… Get Me Out Of Here without informing the chief whip first.
However, she was readmitted to the party in May 2013.
She has been embroiled in a string of controversies throughout her tenure as an MP.
In 2009, when MPs’ expenses claims were revealed by the Daily Telegraph, she admitted she had got taxpayers to foot the bill for a lost £2,190 deposit on a rented flat.
The mother to three daughters has also frequently been at odds with what she thought of as her party’s image, memorably referring to David Cameron and George Osborne as “arrogant posh boys”, while describing herself as “a normal mother who comes from a poor background and who didn’t go to a posh school”.
Having sold more than 2.5 million copies of her books, the 65-year-old’s departure from Government is expected to enable her to return to writing.