Ryanair chief people officer, Eddie Wilson, will succeed Michael O’Leary as chief executive of the group's main airline.
In a restructuring move, Ryanair has become a holding group company comprising several airlines including Ryanair, its Austrian unit Lauda, Poland's Buzz, and Malta Air.
As part of the move, O’Leary will become overall chief executive of Ryanair Holdings with Wilson taking over as chief executive of Ryanair, the biggest carrier within the group.
The restructuring takes place as Ryanair prepares to cut up to 900 jobs across the group, faces fallout from Brexit and has seen a delay in the delivery of Boeing's 737 Max - which has hampered the group's growth plans.
In a note to staff, O'Leary said: "We hope he will build on the successful improvements that the airline has delivered over the last 12 months, particularly as we enter into very difficult times."