Ryanair is setting up its 23rd European base at George Best Belfast City airport.
From the end of October the airline will operate a four times daily service to London Stansted and a new second daily service from Belfast to Liverpool.
Ryanair said the airport approached them last week following the departure of Air Berlin.
Ryanair CEO Michael O' Leary said he expected the new route from Belfast would be more profitable and attract more customers, than Aer Lingus' planned service from Belfast International Airport to London Heathrow.
The airline claims that its arrival will end what it called the 'high fare stranglehold' imposed by British Midland and Easyjet.
