Ryanair will move to fully allocated seating on all its flights from next year.
The budget airline is introducing the measure in response to complaints from passengers fed up with the rush on boarding to get the best seats.
From February 1, travellers can pay five euros (£4.23) to select a specific seat when checking-in more than 24 hours before departure, or pay nothing and be automatically allocated a seat during the 24 hours prior to departure.
Ryanair said in a statement: "Ryanair’s decision to launch fully allocated seating is also part of the airline's commitment to listen to its customers."
The announcement came as Ryanair today issued a second profit warning in as many months, after revealing a profit rise of just 1 per cent to 602 million euros (£510 million) in the six months up to September 30.
The Irish carrier has now slashed its profit forecast for the year to March 31 to 500 million euros (£423.3 million). It made 569 million euros (£487 million) in the year to March 31, 2013.
Following the news, Ryanair shares plummeted 11 per cent to 5.4 pence early this morning.
Last month, the airline announced it is introducing eight new routes from Shannon airport (see news, October 24).