The president has repeatedly downplayed the threat of the virus, even as more than 200,000 Americans have died, but experts have warned that at 74 he is already at a higher risk of falling seriously ill.
Here’s what we know so far:
Who takes over if Trump is too ill to work?
The Trumps have some of the best healthcare in the US available to them, but the president – who is 74 – is still at a higher risk of severe illness than most due to his age, according to the Centres of Disease and Control (CDC) guidelines.
The organisation says people aged 65 to 74 have a five times higher risk of hospital admission with coronavirus compared with those aged 18 to 29, and a 90% higher risk of death.
If Trump became too ill to work, vice president Mike Pence would then take charge.
With a number of cases of Covid reported within the White House, it is feasible that Pence could also test positive. If he did contract the virus, and was incapacitated, the Speaker of the House – democrat Nancy Pelosi – would take over.
What does this mean for the election?
Trump has held large – often maskless – events throughout the pandemic in the lead up to the presidential election and has repeatedly sought to downplay the virus, despite more than 200,000 Americans dying with Covid-19.
He has been fiercely criticised for his approach to the large gatherings, which have attracted crowds of thousands against health guidelines followed worldwide.
But having tested positive for the virus and therefore self-isolating, the Trump’s have been forced to cancel all of their upcoming engagements.
The future of Trump’s planned rallies remains uncertain with the president unlikely to be able to attend events in Wisconsin, Florida and Arizona, the Express reported.
It is also unclear whether or not Trump’s positive test will prevent him from attending the second presidential debate, set to take place on October 15 in Miami, Florida.
With the election itself just 32 days away, Trump’s positive diagnosis raises huge questions around how the event will play out.
The White House has so far made no suggestion of the election being delayed on November 3.
How has the world reacted?
Global markets dropped in the wake of the announcement of Trump’s positive test, with shares and oil prices sinking both in the US and Asia.
With the news breaking early on Friday morning, most world leaders – at the time of writing – had not yet responded publicly to the news.
Boris Johnson, who has recovered from Covid-19 after falling seriously ill, tweeted: “My best wishes to president Trump and the first lady. Hope they both have a speedy recovery from coronavirus.”
US vice president Mike Pence was one of the first to react to the news, tweeting: “Karen [second lady of the United States] and I send our love and prayers to our dear friends president @realDonaldTrump and @FLOTUS Melania Trump.
“We join millions across America praying for their full and swift recovery. God bless you president Trump & our wonderful first lady Melania.”
Indian prime minister Narendra Modi tweeted: “Wishing my @POTUS @realDonaldTrump and @FLOTUS a quick recovery and good health.”
Housing secretary Robert Jenrick told Times Radio that Donald and Melania Trump’s Covid-19 diagnosis is a reminder that everyone is susceptible to the disease and urged the public to follow the rules.
Meanwhile, Wales’ first minister said he believes there will be “political ramifications” following Trump’s positive test.
“This is a president who has always downplayed the virus, acted – as you’ve seen in those rally pictures you were showing – as though it didn’t exist and this is bound to make people in the United States wonder about the quality of the leadership they’ve been offered over the last six months,” Mark Drakeford told Sky News.
He said that “on a personal level” he hoped Trump and the first lady would “sail through” the virus.
“But I think it will bring a whole series of questions to the fore which the president has tried to sideline during this election campaign,” Drakeford said.
“He’s not wanted to talk about coronavirus despite the 200,000 people who have died in the United States. So I think the political ramifications will be real, however his own condition develops.”
What have the Trumps said?
The president announced his diagnosis on Twitter early on Friday morning, writing: “Tonight @FLOTUS [first lady of the United States] and I tested positive for Covid-19. We will begin or quarantine and recovery process immediately.
“We will get through this TOGETHER!”
The first lady later also tweeted, confirming that both she and the president had tested positive as had “too many Americans... this year.”
She added: “We are feeling good and I have postponed all upcoming engagements. Please be sure you are staying safe and we will all get through this together.”
None of Trump’s four adult children, all of whom attended the presidential debate on Tuesday but refused to wear masks, have yet publicly responded to the news.
Who else in the White House has tested positive?
The Trumps are not the first in the White House to test positive for Covid-19 – they themselves took tests after one of his closest aides Hope Hicks was confirmed to have contracted the virus.
While waiting for the results of his test following Hicks’ diagnosis, Trump said he had found it difficult to socially distance while meeting members of the armed forces.
He told Fox News: “It’s very hard when you’re with soldiers, when you’re with airmen, when you’re with the marines, and with the police officers, I’m with them so much.
“And when they come over to you it’s very hard to say ‘stay back, stay back’ you know, it’s a tough kind of a situation, it’s a terrible thing.”
He added: “They come over to you and they want to hug you and they want to kiss you because we really have done a good job for them and you get close and things happen.”
Katie Miller, press secretary to the vice-president, who is married to Trump’s adviser Stephen Miller, has previously recovered from Covid-19.
In May it also emerged that one of Trump’s personal valets had tested positive for Covid-19.