The Labour leader is not showing any signs of symptoms after coming into close contact with someone who tested positive for the virus. Sir Keir will be working from home.
A spokesperson said: “Keir is well and not showing any symptoms.
“He will now be working from home.”
Back in September, the Labour leader went into self-isolation after one of his children showed symptoms.
After his child’s test came back negative, Sir Keir returned to normal duties.
This comes just weeks after Prime Minister Boris Johnson was also forced to self-isolate.
Last month, the Prime Minister had to self-isolate after an MP tested positive for the deadly virus.
Writing on Twitter at the time, Mr Johnson said: “Today I was notified by NHS Test and Trace that I must self-isolate as I have been in contact with someone who tested positive for COVID-19.
“I have no symptoms, but am following the rules and will be working from No 10 as I continue to lead the government’s pandemic response.”
A No 10 spokesman said the Prime Minister did not have any symptoms.
In a WhatsApp message to Tory MPs seen by the BBC the PM added: “The good news is that NHS Test and Trace continues to improve.
“The bad news is that I have been pinged!
“It doesn’t matter that I feel fine – better than ever – or that my body is bursting with antibodies because I have already had the damn thing.
“The rules are the rules and they are there to stop the spread of the disease.”
This is a breaking story. More to follow…