Once the "political craziness" in Britain has played itself out, Europe's largest low-cost carrier does not expect an impact on its business, O'Leary said at a Reuters Newsmaker event in London.
"If you look out long enough, I don't think Brexit has any effect on our business," O'Leary said, on the basis that ultimately Britain would have no choice but to make a trade deal and retain the Open Skies aviation agreement with the EU.
"It's nuts to leave (the EU), but if you are going to leave, the first thing you've got to do on the day after you leave is renegotiate a trade deal with the European Union."
O'Leary campaigned for Britain to remain in the EU in the June 2016 referendum and was one of the most vocal airline executives highlighting the risks of Brexit to the sector.
Since then, Britain and the European Union have agreed a deal to allow flights to continue in the short-term and O'Leary has come to the conclusion that the damage of a British no-deal exit would be too severe.
"I don't think there's anybody who would want to be the UK Prime Minister who leads the UK out on a no-deal scenario. There will be food shortages, there will be medicine shortages," he said, adding that ports would also be disrupted.
"It's going to fall apart at Dover and Calais. And I can't imagine that even (Boris) Johnson would want to be the Prime Minister who visited that on the UK."
But long-term optimism does not diminish the threat of uncertainty in the coming weeks, he said.
"Am I confident of anything in the next 5-10 weeks? No. I have no idea what's going to happen," he said, adding that the government would ultimately be forced to return to a deal along the lines of that brokered by former British Prime Theresa May but rejected in parliament.
O'Leary, who lives around 80 kilometres (50 miles) from the Northern Ireland border said any introduction of border infrastructure could lead to violence.
"I'm not sure how you can go back to checks... anywhere, on the border, 5 miles away from the border, that won't ultimately become a target for a tiny minority of misguided individuals," he said.
"We should be very careful," he added.
(Reporting by Conor Humphries and Tim Hepher; writing by Alistair Smout; editing by Laurence Frost and Jason Neely and Kirsten Donovan)
By Conor Humphries and Tim Hepher