Ryanair is to open a new base at Belfast International Airport, starting in March.
The airline, with an investment of $100m, will base one plane in Belfast and will start a four times daily service to London Gatwick.
Ryanair said the base will grow to three planes and five more new routes from October 2016.
It said this will deliver over 1 million new customers a year at the airport, while it will support 750 jobs there.
Ryanair previously operated flights from the George Best Belfast City Airport between 2007 and 2010 but closed the hub there and pulled out following delays to a planned runway extension.
The airline also said it was adding extra flights from Dublin to London Gatwick as part of its expanded summer 2016 schedule.
It will increase its Dublin to Gatwick service to seven times daily from March, up from its five times a day service.
From March, Ryanair will operate 18 daily flights to London airports - Gatwick, Stansted and Luton - in total as part of its summer schedule. It will also operate three new routes to Amsterdam, Athens and Vigo.
The airline will also operate more flights on 14 other routes including Berlin, Birmingham, Liverpool and Madrid.
Earlier, Ryanair said it carried a total of 101.4 million passengers last year, up 17% on the numbers for 2014.
The airline said it is the first airline to carry over 100 million international passengers in one year.
Its December traffic figures, released this morning, show that passenger numbers were up by 25% during the month to 7.5 million from 6 million the same time last year.
The airline's load factor - how many seats it fills on each flight - also rose to 91% in December from 88% the same time last year.
It also noted that its traffic growth in December of this year is up over 50% from its December 2013 figure of 5 million.