Oneworld has confirmed Air Berlin will officially join the alliance on 20 March, with subsidiary Niki also joining as an affiliate member.
Austrian airline Niki, a subsidiary of the Air Berlin group, will also join Oneworld as an affiliate member.
Air Berlin's membership will add almost 70 destinations to the alliance's map, extending Oneworld's global coverage to around 840 destinations in 150 countries.
Since accepting an invitation to join the alliance in July 2010, Air Berlin has implemented codesharing agreements with seven established Oneworld partners - American Airlines, British Airways, Finnair, Iberia, Malev Hungarian Airlines, S7 and Royal Jordanian.
Air Berlin will become part of the alliance three months ahead of its move into the new Brandenburg airport at its Berlin home, which will open on 3 June with an eventual capacity for 27 million passengers a year, said the airline.
Air Berlin and its alliance partners will be co-located at Europe's newest hub, sharing lounges and many facilities.