British Airways sponsored Air Berlin's entry into the alliance, along with the Oneworld central team. Air Berlin received approval to join the alliance after successfully completing a thorough review of its readiness, conducted by British Airways.
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, said the airline.
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.
It 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.