Watch: Priti Patel quits as Home Secretary as Truss elected new Tory leader
Suella Braverman is considered by bookies to be the favourite to replace her.
Also departing is Nigel Adams, minister without portfolio, who has been a cabinet minister since 2021.
Ms Patel is not a political ally of Ms Truss and commentators have said she was unlikely to have a place in the cabinet of the next prime minister.
The Witham MP did, however, support the foreign secretary’s campaign since mid-July having ruled out running for the top job herself.
She published her resignation letter on Monday night.
It has been the honour of my life to serve as Home Secretary for the last three years.
I am proud of our work to back the police, reform our immigration system and protect our country.
My letter to Prime Minister @BorisJohnson 👇🏽 pic.twitter.com/seTx6ikX25
— Priti Patel (@pritipatel) September 5, 2022
The two page document was largely a celebration of her changes and did not give any clear reason as to her departure.
Addressing Boris Johnson, she wrote: “We have made our country safer, strengthened our law and order, delivered on our manifesto commitments, and laid strong foundations.”
Mas Patel had been home secretary since July 2019 and, as a Brexit supporter, was seen as a closer ally of Boris Johnson and a key figure on the party’s right.
She will be best remembered for her controversial policy of deporting some migrants to Rwanda after she struck a deal with the east African country’s government.
On this, she said in the letter: “The partnership with Rwanda is part of a wider strategy, which includes domestic reform to build Greek-style reception centres in the UK to detain and remove migrants.”
Ms Patel wrote: “I congratulate Liz Truss on being elected as our new leader and I will give her my support as our prime minister.
“It is my choice to continue public service to the country and the Witham constituency from the backbenches, once Liz formally assumes office and a new home secretary is appointed.
“From the backbenches, I will champion many of the policies and causes I have stood up for both inside and outside of government.”
Nigel Adams, the Selby and Ainsty MP, previously announced his intentions not to stand at the next general election.
And with one bound he was gone! pic.twitter.com/8gOYKQKHMY
— 💙 Katharine Parker 🇺🇦Slava Ukraini🇺🇦 (@PenguinOfEurope) September 5, 2022
He tweeted his own resignation letter around the same time as Ms Patel which, like his party colleague’s, was two pages filled with references to the government’s achievements.
Addressing Boris Johnson, he wrote that it would be important for the new prime minister to “build a team that they would like” rather than inherit.
Signing off the letter, he added: “One thing for sure is that there has never been a dull moment along the way and I am honoured to call you my friend.”