United will begin daily Boston-London Heathrow service later this year, at a date to be determined.
The launch date will be based upon demand recovery and when travel restrictions are loosened, Patrick Quayle, United's vice president of international network and alliances, said.
The announcement follows by just one day JetBlue and American's revelation that they will kick off their Northeast Alliance on Feb. 25 with nearly 80 codeshares from the Boston and New York/New Jersey area. Under the alliance, JetBlue will feed domestic passengers to American's transatlantic operations in the Northeast.
United's newly planned London route could also be viewed as a response to JetBlue's intent to inaugurate transatlantic service later this year. The carrier has said it will fly to London from Boston and New York JFK, offering an expanded and upgraded Mint business-class cabin with 24 seats, each featuring sliding privacy doors.
United plans to counter with its own sizeable business-class offering. The carrier said it would deploy a Boeing 767-300ER for the service, with 46 Polaris business-class seats and 22 Premium Plus seats.
"The aircraft features the highest proportion of premium seats on any widebody aircraft operated by a U.S. carrier between London and the United States," United said.
United currently flies to Heathrow from Newark, Washington Dulles and Chicago O'Hare.
Prior to the pandemic, the carrier also flew to London from Denver, Houston Bush Intercontinental, Los Angeles and San Francisco, according to Cirium data.
Boston will be the only non-United hub from which it flies to the U.K.