The deal will give advertisers access to a fleet of 140 new Boeing 737-800 aircraft being currently being delivered to Ryanair over the coming months.
Edinburgh-based Inflight Media has been appointed by Ryanair to handle the project.
Advertisers will be able to buy the space for a minimum of two years, at a starting rate of around £100,000 per aircraft each year.
Ryanair has four existing aircraft that operate on internal flights in Ireland that have been branded by car rental firm Hertz, mobile phone giant Vodafone, car company Jaguar and alcohol brand Kilkenny.
The new package is the first time international flights have been branded by an advertiser.
Stephen Kiggins, managing director of Inflight Media, said: "This is a chance for forward-thinking companies to capitalise on the boom in air passenger numbers and promote their brand to a new European audience in a unique and exciting way."
It is expected that each aircraft will make up to eight flights per day between various European destinations.
Santina Doherty, Ryanair's head of advertising and ancillary revenue, said: "This deal represents a unique opportunity for advertisers to reach Ryanair's 35 million passengers this year, along with tens of millions of passengers at our 107 airports throughout Europe.
"It's an innovative way of generating additional revenue to keep our fares the lowest in Europe."