Philadelphia has become the first of two new transatlantic routes to be started by Aer Lingus for the summer.
Seattle follows in May as the airline’s 15th direct route from Ireland to North America.
Philadelphia will be served by a Boeing 757 four times a week from Dublin, rising to a daily frequency from May 18.
The route expansion follows investment by Aer Lingus owner International Airlines Group in new aircraft, enabling five new transatlantic routes to be introduced the last two years to Los Angeles, Newark, Hartford, Miami and Philadelphia.
Aer Lingus is running its largest long-haul flight schedule with 2.75 million seats across the Atlantic this summer.
Additional transatlantic expansion includes a daily service to both San Francisco and Los Angeles as well as twice daily flights to Chicago.
Miami will continue to be served into next summer operating three times a week while Orlando has four flights a week
Daily flights to Washington will continue to operate this summer with 31% increased capacity through the deployment of a larger Airbus A330-300 on the route for four out of seven days a week.
Passengers travelling from Dublin airport can pre-clear US Customs and Immigration.