The action comes just three months after the airline recommenced flights from Belfast City after an absence of 11 years.
Ryanair operates routes to Malaga, Alicante, Krakow, Warsaw, Gdansk and Milan from Belfast International.
A spokesman for the airport said: “It is disappointing that Ryanair has now decided to withdraw operations from the entire Northern Ireland market at the end of October, having variously had a presence in all three local airports in recent years.
“It has been a difficult period for aviation and a time when consumers need some stability and faith in the Northern Ireland air transport network.”
Earlier on Tuesday, chief executive Michael O’Leary said the airline was set to hit its target of carrying between 90m and 100m passengers for the year to March 2021. It flew 149m passengers in the year to March 2019.
Shares rose jumped 2.1pc to €16.41 in London, valuing the airline at €18.6bn.