The agency won the business, which moves from DDB UK, without a pitch. It is the first account to be picked up by the new agency.
Star Alliance includes brands such as bmi, United Airlines and Lufthansa.
Last year, DDB created a pan-European campaign for Star Alliance that promoted global travel. The TV, print, online and social ads focused on the "Biosphere Connections" sustainability project.
In February, DDB created an app for the network that allowed business travellers to earn upgrades and prizes by taking photos.
Atomic London launched at the end of May. The agency's founders are Fox, Jon Goulding, Guy Bradbury and Richard Hill. Atomic London has a "co-operative" relationship with DDB.