Business Secretary Alok Sharma confirmed he tested negative for coronavirus after he appeared ill during a speech in the House of Commons.
The 52-year-old appeared ill while at the despatch box on Wednesday, with footage showing him wiping sweat off his brow as he delivered a statement to MPs.
Writing on his Twitter, Mr Sharma said: “Huge thanks to everyone for their really kind messages over the last 24 hours and my grateful thanks also to the parliamentary authorities and Speaker for their support yesterday.
“Just had results in and my test for #COVIDー19 was negative.”
Business Secretary Sharma became ill just one day after the government scrapped virtual proceedings, forcing MPs to attend Parliament in person if they wish to participate.
The prime minister's spokesperson confirmed that even those who have had Covid-19 must isolate and when pressed on whether the PM would self-isolate for 14 days if told to, he said: “I would expect us to take medical advice and to follow it."
The dispatch box was being wiped down between exchanges, but the scheduled pause after the Bill’s reading went on for longer than expected and journalists were unusually asked to leave the press gallery following Sharma's speech.
Despatch box cleaned after Sharma speech
But Number 10 says it will not review the return to physical-only proceedings, despite concerns that physical meetings could cause Mr Johnson and Rishi Sunak into isolation.
Many MPs had "serious" safety concerns about returning to Parliament, with many criticising the building's set-up as not fit for social distancing.
Despite Mr Sharma falling ill, Brandon Lewis insisted to ITV News that Parliament has reopened "in a manner that follows the guidelines".
He claimed the new system - which sees MPs form a long, winding queue through Parliament in order to vote - ensures "proper good social distancing and protects people's health and safety".
"Although that does mean we have to queue a little bit to vote, I think it's right that we do that and the least we can do is queue up for a little bit to ensure that we are properly governing the country.
"That is actually, in the long run, hugely important for whole of the United Kingdom," he added.
But Labour's shadow foreign secretary said social distancing in the House of Commons is "impossible".
Lisa Nandy, who lost the Labour leadership election to Keir Starmer, said: “MPs are travelling home to every part of the country tonight. Reckless doesn’t even begin to describe it.”
She said the new queuing system, which has been set up to replace remote voting, has been a "complete shambles".
"It sends exactly the wrong message to the public about social distancing.”