British Home Secretary Amber Rudd. Photo: AFP
Ms Rudd is due to make a statement in Parliament on Monday, but Downing Street has confirmed she has resigned.
The resignation comes as the government struggles to contain the fallout from the Windrush generation scandal involving the government's treatment of Caribbean immigrants who have been in Britain for decades.
The scandal erupted after it emerged that thousands of immigrants who came to Britain as children and have lived legally in the UK for decades had been wrongly caught up in the government's clampdown on illegal immigration.
Some had lost jobs, pensions and healthcare, while others had been threatened with deportation.
Ms Rudd's handling of the crisis has been heavily criticised, with more than 200 MPs signing a letter accusing her of making up immigration policy "on the hoof".
She twice appeared to give MPs inaccurate information about the government's use of deportation targets.
On Sunday, the Guardian published a letter to Theresa May, in which Ms Rudd set out her "ambitious but deliverable" aim to deport 10 percent more illegal immigrants over the "next few years."
Ms Rudd telephoned the prime minister on Sunday evening to tell her of the decision amid intensifying opposition demands for her to quit.
A No 10 spokesman said: "The Prime Minister has tonight accepted the resignation of the Home Secretary."
- BBC
