Siren PR will handle trade and consumer PR activity following competitive pitch.
The agency has been briefed to increase the airline's profile in the UK and to highlight 'the superior on-board service'.
'The key objective for Siren PR is to remove the common misconception that Air Berlin is a no-frills carrier', said Air Berlin country manager UK & Ireland, Titus Johnson.
According to the company, the airline is Germany's second largest carrier after Lufthansa and Europe's fourth largest airline.
The agency will start work on 1 July.