England’s Chief Medical Officer, Professor Chris Whitty, has also announced he is self-isolating, with all three said to be experiencing mild symptoms.
Mr Johnson shared the news on Twitter, saying: “Over the last 24 hours I have developed mild symptoms and tested positive for coronavirus.
“I am now self-isolating, but I will continue to lead the government’s response via videoconference as we fight this virus.
“Together we will beat this. #StayHomeSaveLives”
Over the last 24 hours I have developed mild symptoms and tested positive for coronavirus.
I am now self-isolating, but I will continue to lead the government’s response via video-conference as we fight this virus.
Together we will beat this. #StayHomeSaveLives pic.twitter.com/9Te6aFP0Ri
Mr Johnson has been in a number of high-profile briefings this week with Mr Hancock and Professor Whitty.
Shortly afterwards Mr Johnson’s diagnosis, Mr Hancock revealed he too had the disease, raising questions about the extent of the spread in Westminster.
“Following medical advice, I was advised to test for #coronavirus,” he said online.
“I‘ve tested positive. Thankfully my symptoms are mild and I’m working from home & self-isolating.
“Vital we follow the advice to protect our NHS & save lives.”
Following medical advice, I was advised to test for #Coronavirus.
I‘ve tested positive. Thankfully my symptoms are mild and I’m working from home & self-isolating.
Vital we follow the advice to protect our NHS & save lives#StayHomeSaveLives pic.twitter.com/TguWH6Blij
While Professor Whitty has not been tested, he said he would be self-isolating for the next seven days.
“I will be continuing to advise the government on the medical response to coronavirus, supported by my deputies,” he said on Twitter.
After experiencing symptoms compatible with COVID-19 last night, in line with the guidance, I will be self-isolating at home for the next seven days.
I will be continuing to advise the Government on the medical response to Coronavirus, supported by my deputies.
A spokesperson for Mr Johnson confirmed he spoke with US President Donald Trump on Friday.
“The President wished the Prime Minister a speedy recovery from coronavirus,” the spokesperson said.
“They agreed to work together closely, along with the G7, the G20, and other international partners, to defeat the coronavirus pandemic.”
A Downing Street spokesperson said the Prime Minister experienced “mild symptoms” on Thursday.
“The test was carried out in No 10 by NHS staff and the result of the test was positive,” it said.
“In keeping with the guidance, the Prime Minister is self-isolating in Downing Street.
“He is continuing to lead the government’s response to coronavirus.”
Mr Johnson held his weekly audience with the Queen via telephone this week.
Mr Johnson’s partner, Carrie Symonds is pregnant with her first child which is due early summer.
UK Health Minister Nadine Dorries and Prince Charles have already tested positive to coronavirus in the UK, where it has claimed more than 700 lives.
UK residents are currently being held in a strict lockdown and advised only to leave the house for shopping, exercise or essential work.
In his video address, Mr Johnson said his condition was “mild” and he had a “temperature and a persistent cough.”
“And, on the advice of the Chief Medical Officer, I’ve taken a test. That has come out positive.”
“So I am working from home. I’m self-isolating. And that’s entirely the right thing to do. But be in no doubt that I can continue, thanks to the wizardry of modern technology, to communicate with all my top team to lead the national fightback against coronavirus.
“And I want to thank everybody who’s involved, I want to thank, above all, our amazing NHS staff. It was very moving last night to join in that national clap for the NHS.
“But it’s not just the NHS, it’s our police, our social care workers, teachers, everybody who works in schools, DWP staff.
“I want to thank everybody who’s working to keep our country going through this epidemic. And we will get through it. And the way we’re going to get through it is, of course, by applying the measures that you’ll have heard so much about.
“And the more effectively we all comply with those measures, the faster our country will come through this epidemic and the faster we’ll bounce back.
“So thank you to everybody who’s doing what I’m doing, working from home, to stop the spread of the virus from household to household.
“That’s the way we’re going to win, we’re going to beat it, and we’re going to beat it together.
“Stay at home, protect the NHS, and save lives.”
Previously the government has said that Mr Johnson had the option to delegate to Foreign Secretary Dominic Raab if needed.
So far, 761 people in the United Kingdom have died after testing positive for coronavirus and the number of confirmed cases has risen to more than 14000. The UK toll is the seventh worst in the world, after Italy, Spain, China, Iran, France and the United States, according to a Reuters tally.