McGregor appeared in the briefing room alongside press secretary Karoline Leavitt, where he criticised his country’s government as having “abandoned the voices of the people of Ireland”.
He said there was “zero action with zero accountability,” and complained about the “illegal immigration racket”.
“So the issues need to be addressed, and the 40 million Irish-Americans, as I said, need to hear this,” he said.
“And I’m here to raise the issue and highlight it. As you know, it’s also St Patrick’s Day, so let’s celebrate a little bit.”
McGregor has faced legal problems of his own.
He was ordered by a civil court in Ireland to pay €250,000 Euros (about $427,800) to a woman who sued him for sexual assault.
McGregor denied the accusations.
His comments come days after Irish Prime Minister Micheál Martin visited the White House to meet with Trump.
During the visit, a reporter asked the US president about his favorite Irishman.
“Oh, there are so many… Really? Well, I happen to like your boxer; he has the best tattoos I’ve ever seen. Conor’s great, right? I’m talking about Conor,” Trump said.
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Martin also responded following McGregor’s remarks in the White House.
“St Patrick’s Day around the world is a day rooted in community, humanity, friendship and fellowship,” he wrote on X.
“Conor McGregor’s remarks are wrong, and do not reflect the spirit of St Patrick’s Day, or the views of the people of Ireland.”