The controversial airline boss made the pledge at a tourism conference in Ireland.
Only a shortage of suitable aircraft is delaying the budget airline’s introduction of flights between Europe and America.
But O’Leary is confident the service will be available within the next five to 10 years, according to the Daily Mail.
He told delegates to a hotel conference in Meath that Ryanair would be able to fly to the US during his time as Chief Executive.
O’Leary said: “We’ve had a business plan ready to roll for a transatlantic, low-fares airline.
“The difficulty is, I keep cautioning, is that there’s no availability of long-haul aircraft for another four or five years.
“So unless we can secure a fleet of low-cost aircraft, frankly, the business doesn’t get off the ground.
“The future is very hard to foretell, it certainly is unlikely to happen within the next five years, but I’d be disappointed if it doesn’t happen within the period, maybe, five to 10 years.”
O’Leary had previously announced that Ryanair intends to offer the cheap flights from between 12 to 14 European cities to the same number of destinations in America.
Flights to Boston and New York would start at $13 with return flights to Europe from the US from as little as $10.
But passengers will to pay extra for everything from meals to baggage.
He said: “We can make money on 99 cent fares in Europe. Not every seat will be $13 of course; there will also need to be a very high number of business or premium seats.
“There is 15 percent of the public who will pay for the frills and you will be mad to switch off from that.”
US airline JetBlue dismissed O’Leary’s plans when they were first announced in March.
CEO Dave Barger said O’Leary’s claims that transatlantic tickets could be sold for $13 one-way to Boston and New York from the UK and other European locations adding: “There’s just no way.
“There’s such hype that comes out of certain airlines.”