It means his meetings with US President Joe Biden today are likely to be cancelled.
Taoiseach Micheál Martin has tested positive for Covid-19 ahead of St Patrick's Day events.
All the travelling delegations were tested for Covid-19 yesterday evening in advance of visiting the White House.
The Taoiseach was negative on that initial antigen test, but a member of his delegation tested positive.
Image via Facebook.com/michealmartintdAs a precaution, Micheál Martin was sent for a PCR test which returned a positive result.
He was whipped away from the Gala Ireland Funds Dinner shortly after the starter was served, having heard US President Joe Biden address the gathering.
Micheál Martin and House Speaker Nancy Pelosi had been sitting next to each other without masks.
Pelosi turns 82 next week.
The meeting between the Taoiseach and the US President may now happen virtually instead.
They're due to discuss the war in Ukraine as well as business and cultural relations between Ireland and the US.
The Taoiseach will likely dial in from Blair House, a residence just a few hundred metres from the White House, and the location of Leo Varadkar's famous speech where he shut the schools two years ago.
