The seasonal service is due to start on May 31 and will see Germanwings fly once a week on Saturdays between Ireland West Airport Knock and Cologne-Bonn. The route will operate until the end of October next year.
It's the first service for Germanwings in Ireland outside of Dublin. It flies from the capital to both Cologne-Bonn and Dusseldorf.
Lufthansa has operated a seasonal service between Knock and Dusseldorf for the past two summers.
The chief executive of Tourism Ireland, Niall Gibbons, said the agency would work closely with Germanwings and the airport to maximise the potential of the new service.
Over 400,000 Germans visit Ireland each year with more than 200,000 visiting the west and north west. The new Germanwings service will add an extra 9,000 seats to and from Germany next summer, and bring an estimated 4,000 German tourists to the region.
It's estimated they'll spend more than €2m in the west, north-west and midlands regions.
"Over the coming months, we will be rolling out a comprehensive programme of co-operative promotions in Germany in conjunction with Germanwings," he said.
The airport's managing director, Joe Gilmore, welcomed the new service and said it would be a major boost for tourism in the region.
The new service also adds to a number of new routes that have been secured by Knock.
Ryanair will open new routes to Eindhoven in the Netherlands, Kaunas in Lithuania, and to Glasgow Prestwick from next April after the travel tax is scrapped. Services to London Luton will be increased from 16 flights a week to 18.7.
That's expected to boost Knock's annual passenger traffic to 750,000, from about 670,000.
UK regional airline Flybe has recently launched a new service from Knock to Birmingham.