While at Stokes Kennedy Crowley, O'Leary had met Tony Ryan, head of Guinness Peat Aviation (GPA), a leasing company.

"[13] The business model envisioned by O'Leary uses receipts from onboard shopping, internet gaming, car hire and hotel bookings to supplement the ticket revenue from selling airline seats.

[22][23][24][25][26] His abrasive management style, ruthless pursuit of cost-cutting and his explicitly hostile attitude towards corporate competitors, airport authorities, governments, unions and customers has become a hallmark.

In the airline industry there are so called slots or sometimes gates, often regulated by law, and without obtaining them it is impossible to have regular service to airports).

Despite his claims in 2002, there were so called budget airlines in the past who serve long haul routes – for example Laker Airways flights from London to New York in the late 1970s or long-hauls at budget-fares on other continents like AirAsiaX in Malaysia and the Australian Jetstar Group.

[34] He has been reported to have impersonated a journalist in an attempt to find information passed on to a newspaper following a safety incident on a Ryanair flight.

Aer Lingus, whose biggest shareholder at the time was Ryanair, had to cancel 200 flights and disrupt travel plans for 200,000 people.

In February 2020, O'Leary suggested that airport security should focus on single Muslim men and called obese passengers "monsters".

[44] In June 2022, O'Leary defended Ryanair's use of an Afrikaans language test on South African nationals flying to the UK and Ireland.

[47] In 2010, O'Leary stated that he thought the scientific consensus on human-caused global warming was "horseshit" in an interview with the Irish Independent.

When asked whether that climate change is happening, O'Leary replied that the cooling and warming had been "going on for years" and did not accept it was linked to carbon usage.

[49] In 2021, he was less dismissive and said "it is something that our customers and the people working here at Ryanair wants us to focus on and we tend to be very responsive.“[50] O'Leary married Anita Farrell on 5 September 2003 in Delvin, County Westmeath,[51] with whom he has four children.

He had the opportunity to buy a stake in the club in 2003, but believed the potential benefits did not outweigh the risk, and preferred instead to visit England to watch a few matches each season.