In a video posted on Twitter, 55-year-old Johnson said, "over the last 24 hours I have developed mild symptoms and tested positive for coronavirus" in a tweet.
Johnson also said that he is self-isolating himself and would "continue to lead the government's response via video-conference".
Work from home
A Downing Street spokesperson said in a statement that Johnson, whose partner Carrie Symonds is pregnant, experienced mild symptoms on Thursday and was tested for COVID-19 on the personal advice of England's chief medical officer.
While it isn't clear yet from whom or where the UK PM got infected, as he has been working from home over the last few days, Johnson has been seen addressing the nation through television while standing beside senior officials.
Johnson's last meetings
Since the outbreak, Johnson has met his Finance Minister Rishi Sunak, Dominic Cummings and Chief Scientific Adviser Patrick Vallance.
The infection also raises concerns over Johnson's fiancee, Carrie Symonds, who is pregnant. and is still living with Johnson.
Johnson was last seen on Thursday night, clapping outside his house at Downing Street as part of a nationwide gesture to thank NHS staff.
Johnson held the first of a series of daily press briefings on coronavirus. During the televised briefing, Johnson addressed the Britons while standing beside senior officials.
Johnson chaired a Cobra meeting on coronavirus with medical experts and ministers to sketch out a plan against the rapidly spreading virus.
A Buckingham Palace spokesman confirmed the Queen saw Mr Johnson. The pair usually meet weekly for, but the most recent meetings have been over the phone due to the pandemic.