Ryanair will roll out its reservation option for certain seats, which has been trialled on select routes since May, to the entire network in January.
Over the past six months, passengers have been able to purchase reservations for the seats in the front two rows and at the over-wing exits for £10 ($15.70) per flight on around 100 routes.
While the first rows allow quicker debarkation after arrival, the seats at the emergency exits offer more leg room.
The scheme has been so popular that it will be extended to the entire network from 10 January, the Irish budget airline said.
The company operates approximately 1,100 routes, according to its website.
Earlier this month, UK low-cost carrier EasyJet revealed that it would trial allocated seating on selected routes from next spring.