A Downing Street spokesperson said the Prime Minister experienced “mild symptoms” on Thursday and was tested on the advice of England’s Chief Medical Officer, Professor Chris Whitty.
“The test was carried out in No 10 by NHS staff and the result of the test was positive.
“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 500 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 Johnson had the option to delegate to Foreign Secretary Dominic Raab if needed.
So far, 578 people in the United Kingdom have died after testing positive for coronavirus and the number of confirmed cases has risen to 11,658. 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.