Virgin Atlantic will launch direct services from Belfast to Orlando and from Glasgow to Las Vegas next summer.
The British carrier will be the only scheduled airline to fly both routes, it said.
The Belfast to Orlando service will mark the first time Virgin Atlantic has operated out of Northern Ireland, while the Glasgow to Las Vegas route is the first time the airline has flown direct from Scotland to Sin City.
Both routes will form part of Virgin Atlantic's joint venture with Delta Air Lines (see news, November 2013), with the US carrier offering the service for sale under a codeshare agreement.
Craig Kreeger, chief executive of Virgin Atlantic, said: "It's incredibly important to us to offer customers from all across the UK access to our long-haul network during peak travel periods – and now even more people can enjoy the Virgin Atlantic renowned customer experience."
A B747-400 aircraft in a three-class configuration will operate both seasonal services on a weekly basis, flying on Thursdays. It will contain 14 Upper Class (business) seats, 66 in premium economy and 375 in economy.
The Belfast to Orlando route will operate in June and July 2015, starting on June 25. The Glasgow to Las Vegas service will run in September and October 2015, starting on September 10.