"It is my choice to continue my public service to the country and the Witham constituency from the backbenches, once Liz Truss formally assumes office and a new Home Secretary is appointed," Patel wrote in her resignation letter to outgoing PM Boris Johnson.
In her resignation letter addressed to Johnson, 50-year-old Patel highlighted her many achievements in the post, including a Migration and Mobility Partnership signed with India, among other countries, to tackle illegal migration.
I congratulate Liz Truss on being elected our new leader and will give her my support as our new Prime Minister, she wrote in her resignation letter.
"From the backbenches, I will champion many of the policies and causes that I have stood for both inside and outside of government," she said.
I have signed new international returns agreements with India, Albania, Serbia, Nigeria, and Pakistan, with work underway to negotiate more agreements and to remove more people who should not be in this country and who have abused our hospitality, she wrote, with reference to some of her work as the head of the Home Office.
The portfolio of the Home Secretary is expected to be handed to another Indian-origin minister, Suella Braverman.
Gujarat-origin Patel, who was appointed Home Secretary by Boris Johnson in July 2019, described it as the honour of her life to deliver reforms for the country's police and immigration system, and fighting terrorism.
Her letter also references the controversial Rwanda asylum policy to deport illegal migrants to the African nation as part of a wider strategy to crack down on illegal migration.
(With inputs from PTI.)