Ryanair has ordered 300 new Boeing 737-MAX-10 aircraft, worth more than €36 billion.
The carrier has said this is the largest order ever placed by an Irish company for US manufactured goods.
The new planes will be due for delivery between 2027 and 2033.
The deal - which will see the airline buy 150 aircraft with the option for another 150 - will be subject to shareholder approval at Ryanair's AGM in September.
Ryanair has said the phased deliveries will mean creating more than 10,000 new jobs for pilots, cabin crew and engineers.
The company expects 50% of these deliveries will replace older B737NGs.
"This new order will enable Ryanair to deliver sustained traffic and tourism growth at lower fares - and lower emissions per flight - across all European countries where Ryanair continues to lead the post Covid traffic, tourism and jobs recovery," the Irish airline said in a statement.
Ryanair Group CEO Michael O’Leary said this will mean lower fares for passengers.
"In addition to delivering significant revenue and traffic growth across Europe, we expect these new, larger, more efficient, greener, aircraft to drive further unit cost savings - which will be passed on to passengers in lower air fares.
"The extra seats, lower fuel burn and more competitive aircraft pricing supported by our strong balance sheet, will widen the cost gap between Ryanair and competitor EU airlines for many years to come, making the Boeing MAX-10 the ideal growth aircraft order for Ryanair, our passengers, our people and our shareholders".
Boeing President Dave Calhoun praised the 'landmark' deal.
"The Boeing-Ryanair partnership is one of the most productive in commercial aviation history, enabling both companies to succeed and expand affordable travel to hundreds of millions of people.
"Nearly a quarter century after our companies signed our first direct airplane purchase, this landmark deal will further strengthen our partnership.
"We are committed to delivering for Ryanair and helping Europe’s largest airline group achieve its goals by offering its customers the lowest fares in Europe," he added.