Aer Lingus is to transfer its operations to the new terminal at Dublin airport, which is scheduled to open in November.
The company said the move to Terminal 2 would allow its departing passengers to fully clear US immigration, customs and agriculture controls, a facility that is already in operation at Shannon airport.
Aer Lingus said there would be no significant increase in the group's operating costs arising from the move, as long as differential pricing was not introduced at the airport. If that occurred, the company said it would review its decision.
Chief executive Christoph Mueller described the move as "a significant moment in the history of Irish aviation".