The new Aer Lingus service from Belfast International Airport at Aldergrove began this morning with flights to Amsterdam and Barcelona.
It is the airline's first ever base outside the Republic and by next February the company plans to be flying to nine European destinations.
Aer Lingus caused controversy in the west of Ireland when it announced the ending of its Shannon-London service and transferred the slots to Belfast.
Three aircraft will be based at Belfast International at Aldergrove, primarily serving two of Europe's biggest airline hubs: London Heathrow and Amsterdam Schiphol.
There will also be services to other European destinations including Rome, Barcelona and Geneva. The company is investing €150m in the move to Belfast and is creating over 150 new jobs.
It has already sold more than 50,000 tickets on the Belfast routes and plans to carry at least 500,000 passengers from Aldergrove in the first year of operations.
Aer Lingus Chief Executive, Dermot Mannion, said: 'This day marks a new era in flying both for the people of Northern Ireland and Aer Lingus.
'Our investment in three aircraft and 100 jobs in our first base outside the Republic signals our firm intent to develop new markets as the company continues to grow and serve an expanding route network.'
Politicians and business leaders in the west are still angry at Aer Lingus' decision to axe the Shannon-London routes to facilitate its opening in Belfast. The company has repeatedly said it has no plans to re-instate the Shannon services.
The Aer Lingus arrival in Northern Ireland comes just weeks after rival Ryanair began flying from George Best Belfast City Airport to four destinations in England and Scotland.