Priti Patel is to resign as home secretary when Liz Truss takes office as prime minister, Sky News reports.
Writing a letter to Boris Johnson on Monday afternoon, Ms Patel said "it has been the honour of my life to serve our country as home secretary for the last three years", adding that she will now "champion many of the policies and causes I have stood up for" from the backbenches.
Reports on Monday evening suggested that Culture Secretary Nadine Dorries has also told allies that she intends to stand down from her ministerial position on Tuesday.
Ms Truss is due to announce her cabinet on Tuesday after being formally appointed the country's next minister by the Queen.
It has been widely reported that Ms Patel, who has been home secretary since 2019, was not expected to be by Ms Truss to remain in her position.
Ms Patel had not endorsed any candidate during the Tory leadership campaign.
Meanwhile, Stephen McPartland has resigned as security minister saying he now looks forward to supporting Ms Truss "wholeheartedly from the backbenches".
Mr McPartland had only been asked to serve in the role for an interim period and wrote to Mr Johnson that he now wants to "step aside for someone who wants to pursue the role on a more permanent basis".
There is precedent in ministers resigning at the change of a prime minister.
Three years ago, in 2019, then justice secretary and Lord Chancellor David Gauke quit Theresa May's top team after Mr Johnson won the Tory leadership battle.
Source: Sky News