Leo Varadkar also thanked President Trump for his support of a new E3 visa programme which, if passed by Congress, would benefit Irish citizens who wish to work in the US.
Today the Taoiseach will leave Washington and travel to Chicago to meet emigrant support groups.
He was surprised how badly the Brexit talks had gone, adding: "I gave the prime minister [Mrs May] my ideas on how to negotiate. she didn't listen to that and that's fine".
Ahead of that make or break moment, United States president Trump gave his take on how well things are going. "I predicted it was going to happen".
"I think it could've been negotiated in a different manner, frankly".
That's a subtweet if I've ever seen one.
If they don't, the UK faces a hard exit from the European Union, an eventuality many officials in the US, UK and Europe believe could cause economic turmoil.
"They'd say: 'What do you mean you've gotta take another vote?' So that would be tough".
The most concerning element for Ireland, Varadkar said, is that Brexit should not cause any problems in Northern Ireland, which voted to stay in the EU.
Nile Gardiner, a former aide to British prime minister Margaret Thatcher and director of the Margaret Thatcher Center for Freedom at the Heritage Foundation, said Trump "has been very clear in his view that Brexit is great for America and for Britain".
"We talked about Brexit, something that is turning out to be a little more complex than they thought it would be. We're going to tariff a lot of their products coming in because the European Union treats us very, very unfairly".
After the meeting, the prime minster said he appreciated the opportunity to lay out Ireland's position on Brexit.
He said: "I know he is a supporter of Brexit and I am not".
But the tensions over Brexit served this year to highlight a divide between the two countries with Ireland embracing the E.U.as Trump questions why European nations continue to marry their economies together instead of going it alone on issues like trade. "There's 500 million of us, only 60 million of them".
Speaking as voting on whether to rule out a no-deal Brexit began at Westminster, Mr Varadkar said: "It's always important to remind ourselves that Brexit.is the decision that the United Kingdom has made, a decision that we deeply regret in Ireland and across Europe".
Last year, Vice President Pence reportedly extended an invitation to Varadkar and Barrett to visit him and his wife Karen at their Washington, DC residence.