Southwest and Icelandair have reached an agreement to launch an interline partnership in February, following through on a memorandum of understanding reached in September.
Initially, the interline itineraries will be bookable only in Icelandair channels, with the shared itineraries connecting in Baltimore. The carriers said they will add Denver and Nashville as connecting points later this year.
Southwest won't begin selling Icelandair segments in its booking channels until it adds assigned seating in 2026, airline executives said in September.
Icelandair will be Southwest's first partner in decades. The airlines launched an alliance in the 1990s that has long since ended.
Southwest has eschewed airline partnerships in this century. But in September, as part of broad plan geared toward improving financial performance, the carrier announced it would change course. The airline said Thursday that it is "actively pursuing additional, like-minded partners to provide more options that meet travel needs on both transatlantic and transpacific routes."
Southwest said it is making the required technology investments to enable partnerships, including rewards program partnerships.