PSG is an independent Irish comms group affiliated to Ketchum.
The agency won the work following a four-way pitch including incumbent agency WHPR, Ogilvy's PR arm in Ireland, which had held the account since 2009. The airline has also worked with Golley Slater in the UK.
The contract will run for two years. The three-part brief covers consumer, CSR and sponsorship.
PSG will work on Aer Lingus’ new sponsorship deal with the Irish Rugby Football Union, ahead of the Rugby World Cup this autumn.
Aer Lingus has also recently hired creative agency KesselsKramer, which has offices in Amsterdam, London and Los Angeles.
Aer Lingus is currently in takeover talks with International Airlines Group (IAG), which owns BA and Iberia. This month the European Commission cleared the £940m takeover by IAG but said it was "conditional".