On Thursday, the Prime Minister held a 35-minute meeting with a group of MPs including Lee Anderson who later tested positive for the virus.
Mr Johnson has no symptoms of Covid-19 and will continue to work from Downing Street, his official spokesperson said.
The PM nearly died during his battle with coronavirus earlier this year. Intensive care doctors at St Thomas’ Hospital in central London plied Mr Johnson with ‘litres and litres’ of oxygen as his chances of survival balanced on a knife-edge.
Under Government guidelines, those who come in to contact with people who test positive must isolate for 14 days.
The Prime Minister was informed he had come into contact with an infected person via the NHS Test and Trace app.
A spokesperson for the PM said: ‘The Prime Minister has today been notified by NHS Test and Trace that he is required to self-isolate as a contact of someone who has tested positive for Covid-19.
‘The Prime Minister will follow the rules and is self-isolating.
‘He will carry on working from Downing Street, including on leading the government’s response to the coronavirus pandemic.
‘The PM is well and does not have any symptoms of Covid-19.’
Prime Minister Boris Johnson must self isolate after being in touch with someone who has tested positive for Covid-19.