Stelios Haji-Ioannou was born in Athens in February 1967 to Cypriot parents Loucas and Nedi. He has an older brother (Polys) and a younger sister (Clelia), who is a plastic surgeon. Both are shareholders in some of Stelios' ventures. Because of their inability to remember foreign names, many British people call him Stavros.

Stelios attended Doucas Greek High School in Athens and took two A-levels. In 1984, he moved to London to study at the London School of Economics where he got a Bsc in 1987 and in the following year he got a Msc in Shipping, Trade and Finance from the City University Business School. He then went into his father's business, Troodos Shipping. In April 1991, a Troodos tanker, the Haven, exploded, killing 5 crew members and creating an oil slick along the Italian coast. Stelios was personally prosecuted by the Italian courts on criminal charges that included manslaughter and extortion. The charges were eventually dropped after many years, but it did mean that easyJet was unable to fly into an Italian airport until the final appeal was heard. Eighteen months later, with a loan from his parents, Stelios founded Stelmar Tankers, which floated on the New York Stock Exchange in March 2001.

In 1995, he founded easyJet, (small e big J) a low-cost, no frills, point to point airline, modelled on America's Southwest Airlines to take advantage of the deregulation of the European airline industry. This wasn't the first idea for his brash orange easy brand. There was an idea at one point to utilise his sister's plastic surgery skills and start a company called easyBooby. Fortunately, it never got off the ground. Early easyJet pioneers were Raymond Webster, who had tried and failed to set up a low-cost airline within Air New Zealand and Nick Manoudakis, an old friend. When easyJet started flying (to Edinburgh and Glasgow) in November 1995, Stelios entered the Guinness Book of World Records as the youngest ever airline chairman. easyJet floated on the London Stock Exchange in November 2000.

Stelios' management style is to keep costs low by eliminating unnecessary costs and utilising modern technologies. This means no secretaries, paperless offices, ticketless travel, almost all bookings being taken over the internet, costs of tickets being determined by an aggressive yield management system and easyJet headquarters being nothing more than a tin shed next to the runway at Luton Airport. Stelios is famed for working 100-hour weeks, and instead of holding sit-down meetings, holds stand-ups in order to save time. He is often to be found on easyJet flights walking the tube, talking to other passengers and can rightly claim to know more about their likes and dislikes than any of his marketing team. Stelios never takes salary, expenses or royalties out of his companies. He is a larger than life figure, his size being helped along by the fact that he always positions himself next to the buffet at easyJet parties. He is known for throwing the toys out of the pram if he doesn't get his way at board meetings. When the rest of easyJet's board delayed signing an agreement to purchase Airbus aircraft to complement and eventually replace the fleet of Boeing 737's, Stelios refused to allow any other resolutions to be passed. He was replaced as easyJet chairman in November 2002, officially so that he could spend more time with his other ventures. A chairman of a public company is supposed to be the one who holds the rest of the board in check; at easyJet it was the other way round.

In 1998, Stelios founded easyGroup to extend the easy brand to other new ventures. These have included easyInternetcafe, which started trading in June 1999, easyCar, an online car rental service, easyValue for online impartial comparisons,, a free web-based email service, easyMoney, an online credit card company and easyCinema, which opened its doors in May 2003. Stelios is a serial enterpreneur, very similar in style to Richard Branson, next to whom he is often photographed. He sees himself as a David figure, fighting off the old Goliaths such as British Airways and Barclays. He has frequently picked fights with them and others and uses these spats to splash the easy brand across newspaper headlines. When British Airways launched Go in 1998 as direct competition to easyJet, Stelios and his team booked themselves on to the inaugural flight and turned up dressed in orange boiler suits. The journalists spent the flight interviwing the overweight Greek rather than Go's rather attractive chief executive.

Stelios continues to take the easy brand into new industries, the latest offerings in the pipeline being easyPizza, easyCruise, easyDorm and easyBus. He lives in his bachelor penthouse overlooking Monte Carlo harbour.