Level is the company’s low-cost transatlantic service, which will operate out of Barcelona.
Today it launched its inaugural flight from Barcelona to Los Angeles, with 314 passengers onboard.
Flights to LA will operate twice weekly and tomorrow the three-times weekly service to San Francisco will start.
The airline confirmed it would increase its fleet to five aircraft in 2018.
Last month, Level announced it had sold more than 100,000 tickets after going on sale for just four weeks.
Willie Walsh, IAG’s chief executive said: “This is the start of a fantastic new adventure for International Airlines Group - the parent company of British Airways and Spain's Iberia which was created by the merger of the two carriers in 2010. Level’s sales are well ahead of our expectations in all markets. The brand has resonated with a new audience, many of whom are flying long-haul for the first time.
Level will operate the service with two new Airbus A330 aircraft branded in its own livery and fitted with 293 economy and 21 premium economy seats.
It will initially be operated by Iberia’s crew and create up to 250 jobs in Barcelona.