White House chief of staff Mark Meadows, who has frequently appeared at public events without wearing a mask, has been diagnosed with Covid-19, a source familiar with the situation told Reuters on Friday.
It was not immediately clear when or how he was infected.
Another top campaign aide, Nick Trainer, has also tested positive for the virus, according to the source.
Meadows, Trump's top adviser and a former North Carolina lawmaker, regularly accompanied US President Donald Trump on the final frenzied days of the campaign rallies leading up to the presidential election on Tuesday.
Meadows, who was at a White House election night party attended by dozens of Trump loyalists, is the latest official within Trump's close circle to have contracted Covid-19, which has killed more than 236,000 Americans.
Trump has regularly downplayed the severity of the virus, which has surged in recent weeks and is poised to continue do so into the winter. He has contradicted the public statements of top health experts, even after an outbreak seized the White House in October.
The president was briefly hospitalised at the time after he was infected with the virus. His wife and son Barron also tested positive for the coronavirus in October.
His national security adviser, Robert O'Brien, was also sickened with the virus. Another friend of Trump's, former Republican presidential candidate Herman Cain, died of the coronavirus in July after attending one of Trump's rallies.