The deal will give advertisers access to one or more of a fleet of new Boeing 737-800 aircraft currently being delivered to Ryanair.
Edinburgh-based Inflight Media has been appointed by Ryanair to handle the project.
Clients will be able to buy the space for a minimum of two years, starting at around £100,000 per aircraft each year.
Ryanair has four aircraft that operate on Irish internal flights 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.
Earlier this year the Kent Messenger group was on the verge of branding an aircraft with no-frills and Kent-based airline EU Jet, only for the airline to halt flights in June.