Defence secretary Gavin Williamson has been sacked after "compelling evidence" emerged that he was responsible for leaking details from a National Security Council meeting to a newspaper.
A Downing Street spokesman said the Prime Minister had "lost confidence" in Mr Williamson's ability to serve as defence secretary, following an inquiry into how information about possible risks to national security over a deal with Huawei were leaked.
In a letter from Theresa May to Mr Williamson, she wrote that there was no other "credible version of events" that explained the leak, and asked him to leave the government.
It has been confirmed that international development secretary Penny Mordaunt will take over his role, and prisons minister, Rory Stewart, will take hers.
"The Prime Minister has this evening asked Gavin Williamson to leave the government, having lost confidence in his ability to serve in the role of defence secretary and as a member of her Cabinet," the Downing Street spokesman said.
"The Prime Minister's decision has been informed by his conduct surrounding an investigation into the circumstances of the unauthorised disclosure of information from a meeting of the National Security Council."
However, Mr Williamson maintains that he was not the source of the leak.
Responding to the Prime Minister with another letter, he said that he "strenuously" denied being responsible.