Italian flag-carrier Alitalia will retroactively join the SkyTeam transatlantic joint venture currently conducted between Air France-KLM and Delta Air Lines.
Alitalia's membership is being considered effective from 1 April this year.
Under the agreement the venture will incorporate 20 daily transatlantic services to five US destinations from Rome and Milan.
Alitalia's Rome Fiumicino hub will become part of the core of the venture - through which the airlines share transatlantic revenues and costs - alongside Paris, Amsterdam and the US cities of New York, Detroit, Minneapolis and Atlanta.
"Transatlantic traffic is the most strategic and competitive marketplace," says Alitalia chief Rocco Sabelli.
"Such an achievement [as joining the venture] highlights the valuable results obtained so far by Alitalia, and further opens-up opportunities for our industrial and commercial growth."
Alitalia's services will bring the joint venture's share of the transatlantic capacity to around 26% and take annual revenues to some $10 billion.
Delta Air Lines says Alitalia's admission to the joint venture is backdated to 1 April 2010 as part of a long-term pact lasting at least to the end of March 2022.
Governance of the joint venture will be shared equally between Alitalia, Air France-KLM and Delta. Alitalia representatives will join the venture's 11 working groups which manage network, revenue management and other critical aspects of the partnership.
Air France-KLM, which has a shareholding in Alitalia, says the venture has been "strengthened" by the inclusion of the Italian airline.
Chief executive Pierre-Henri Gourgeon says Air France-KLM already has agreements with Alitalia on Italian-French and Italian-Dutch routes, and the transatlantic partnership is "therefore natural".
With Alitalia's membership the combined venture will provide nearly 250 transatlantic flights per day. Its scope not only includes all flights between North America and Europe, but also services between Amsterdam and India and between North America and Tahiti.