“This noon one of my children tested positive for Covid,” Sir Keir wrote in a social media post on Wednesday.
“I know it’s my responsibility to follow the rules – my family and I are isolating ourselves now.”
This will affect the launch on Thursday of Labor’s new “Safer Communities” launch, and a party spokesperson said Sir Keir tested negative on Wednesday morning.
“He will continue to take daily tests,” the spokesperson said. “By the rules, Keir and his family will now be self-isolating.”
Sajid Javid, the health secretary, tested positive for the virus on Saturday, which means Mr Javid, Mr Johnson and Rishi Sunak, the chancellor, are also all in isolation.
This is the fourth time Sir Keir has had to self-isolate, the Labor Party has confirmed.
Another member of his family tested positive for the virus in September and one of his parliamentary employees contracted the virus in December.