Deputy Prime Minister Barnaby Joyce believes he contracted COVID-19 in London before flying to Washington DC.
He tested positive after arriving in the United States as part of a 10-day trip focused on the Morrison government's push for tighter social media regulations.
"I was just getting a bit tired and then I started getting ... a couple of pains in the legs so thought I better get tested," he told Sky News from quarantine on Thursday morning, Australian time.
"You really have to quiz yourself as to whether you need to be tested at all, because ... it doesn't scream at you."
Mr Joyce is double-vaccinated. He thinks he contracted the virus in the United Kingdom because he tested negative twice before flying to Washington.
"You wouldn't know there was a pandemic on in these areas of the UK. People are just shoulder-to-shoulder," he said.
The deputy prime minister doesn't know what strain of the virus he has. Those travelling with him have tested negative.
"I hope that in the future, rather than being isolated, this is like the flu. You get it, you go home and you manage it yourself," Mr Joyce said.
"I'm not dying here. I'm feeling like I have a slight-to-mild flu."
Prime Minister Scott Morrison, who has been in touch with Mr Joyce, said it highlighted the importance of getting the jab.
"He (Mr Joyce) tells me he's feeling alright, apart from the mild illness, and he has been vaccinated," Mr Morrison told reporters in Victoria.
"Vaccinations do have an impact on the seriousness of the disease and that's why it's so important to get vaccinated. It's another important reminder and why the booster is also so important."
Opposition Leader Anthony Albanese said he wished Mr Joyce a quick recovery.
"I wish him, and anyone who tests positive for COVID, well," he said.
"I'm sure that he will take appropriate action in terms of isolating."
Deputy Nationals leader David Littleproud spoke to Mr Joyce following the diagnosis.
"He's isolating in the US until it's safe for him to come home and we wish him all the best for his recovery," Mr Littleproud tweeted.
