He is still suffering from the symptoms after being diagnosed 10 days ago with the virus.
His office said that he was admitted to an undisclosed hospital as a precautionary measure as he is not critical.
Johnson, 55, was diagnosed on the 26th of March 2020 and has been in quarantine at the Downing Street residence.
He is the first world leader to have contracted coronavirus.
Johnson was going about business as usual from his self isolation but he said he was feeling better but still had a fever on Friday.
Another quick update from me on our campaign against #coronavirus.— Boris Johnson #StayHomeSaveLives (@BorisJohnson) April 3, 2020
You are saving lives by staying at home, so I urge you to stick with it this weekend, even if we do have some fine weather.#StayHomeSaveLives pic.twitter.com/4GHmJhxXQ0
The virus causes mild to moderate symptoms in most people, but for some, especially older adults and the infirm, it can cause pneumonia and lead to death.
Johnson’s fiancee, Carrie Symonds, 32, revealed Saturday that she spent a week in bed with coronavirus symptoms, though she wasn't tested.
Symonds, who is pregnant, said she was now “on the mend.” She has not been staying with the prime minister in Downing St. since his diagnosis.
The U.K. government said Sunday that almost 48,000 people have been confirmed to have COVID-19, and 4,934 have died.
The Queen made an announcement just before news of Johnson's hospitalization broke.
She urged Britons to remain “united and resolute” in the fight against the virus.
“We will succeed — and that success will belong to every one of us,” the 93-year-old monarch said, drawing parallels to the struggle of World War II.
“We should take comfort that while we may have more still to endure, better days will return: we will be with our friends again; we will be with our families again; we will meet again," she said.