The president's doctor said Biden has received his first dose of Paxlovid, and will be self-isolating at his home in Rehoboth Beach, Delaware, in line with US Centres for Disease Control and Prevention guidance.
"The president presented this afternoon with upper respiratory symptoms, to include rhinorhea (runny nose) and non-productive cough, with general malaise," a note from Biden's doctor Kevin O'Connor provided by White House press secretary Karine Jean-Pierre said.
"He felt okay for his first event of the day, but given that he was not feeling better, point of care testing for COVID-19 was conducted, and the results were positive for the COVID-19 virus."
Biden's symptoms were "mild", with his temperature and breathing rate normal, O'Connor said.
Biden has already boarded Air Force One for the flight to Delaware.
He told reporters traveling with him, "I feel good."
He was not wearing a mask as he walked onto Air Force One.
Jean-Pierre said Biden would continue to fulfil all his duties during his period of self-isolation.
The White House's confirmation followed an announcement at the conference by UnidosUS President and CEO Janet Murguía, after Biden was an hour and a half late to his scheduled appearance in Las Vegas.
"I was just on the phone with President Biden. And he shared his deep disappointment at not being able to join us this afternoon," Murguía told conference attendees.
"The president has been at many events as we all know and he just tested positive for COVID."
Biden, 81, had been scheduled to take the stage an hour and a half prior.
He last tested positive for COVID-19 twice in the summer of 2022, when he had a primary case and a rebound case of the virus.
Health officials have reported recent upticks in emergency room visits and hospitalisations from COVID-19. There has also been a pronounced increase in positive test results in much of the country — particularly the southwestern US.
The news comes after the president publicly defied calls for him to step away from the 2024 presidential election.
A growing number, though still a minority, of Democrats, have said Biden should step down amid concerns over his ability to govern for a second term.
However, Biden, who defeated now-official Republican nominee Donald Trump in the 2020 election, has remained defiant, saying he is still the best person for the job.
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In an interview with BET News this week, Biden said he would only consider dropping out of the race under medical advice.
"If I had some medical condition that emerged, if somebody — if doctors came to me and said you got this problem, that problem," he said.
He said he had no medical conditions the public were unaware of.
With CNN.
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