The budget airline said it became the first European airline to carry one billion passengers since its inception in 1985, launching a huge flash sale in celebration.
Ryanair is offering 20% off one million seats, with tickets starting from £9.99.
In July the group carried 11.3 million passengers, up 11% on the same time last year when it had been month after the UK voted to leave the European Union.
The load factor, the ratio of seats available to passengers carried, climbed one percentage point to 96%.
Ryanair attributed the growth to lower fares and the success of its "Always Getting Better" customer experience programme.
However, things may no longer be getting better for customers or the airline if the government fails to secure a deal with the European Union in its Brexit negotiations before September 2018, Ryanair’s chief executive warned.
Ryanair threatens to pull flights if government fails to secure Brexit deal
Michael O’Leary told a press conference that Ryanair may need to pull flights unless a deal is in place by next year.
“We hope and trust the deal will get done by September 2018,” he told reporters.
“Otherwise we and other airlines will have to start cancelling flights or taking flights off sale for the summer of ’19.”
O’Leary meets with transport minister
O’Leary said he met with transport minister Chris Grayling and stressed the need for an early deal. He vented his frustration that the government seemed to have no fall-back plan.
O’Leary added it was incredibly likely that if the government pursues a ‘hard’ Brexit there will be no bilateral agreement to replace the current open skies regulation that allows EU airlines and other in the common travel area to fly in and out of any country signed up to the pact.
"We would like to see some reasonably speedy conclusion of the pre-negotiations,” O’Leary added.
“The divorce bill, whatever the hell then number is, is there an agreement on it? Then we can start to talk about an agreement."