Ryanair secured an option with Niki Lauda that would allow the Irish airline to take full ownership of Laudamotion in four years.
Ryanair, which expects regulatory approval in coming weeks to take a 75% stake in Laudamotion, already acquired a 24.9% stake in March 2018.
Ryanair also plans to invest another €20 million in the Austrian airline, on top of the €100 million already announced.
Laudamotion begins flights from Vienna on 02 June 2018, with four based aircraft.
Ryanair plans to base with up to 50 planes in Vienna over the coming years.