Grey won the business after a final shoot-out against its sister WPP agency Rainey Kelly Campbell Roalfe/Y&R and CHI & Partners, which is also part-owned by WPP.
The incumbent on the account was the Irish agency DDFH&B. However, it is understood that only WPP-owned or -backed agencies were invited to pitch.
The Vodafone Ireland marketing director, Anne Mulcahy, called the pitch last November. The mobile company's UK business, which is currently held by Bartle Bogle Hegarty, is unaffected by the appointment.
Global strategy for Vodafone has been handled by Team Vodafone, a collaboration of WPP agencies led by JWT, since March 2009. It was previously held by BBH.
Vodafone Ireland is the largest mobile phone company in Ireland in terms of active subscribers. It was formerly called Eircell.
A recent DDFH&B television spot for Vodafone Ireland, called "summer friends", featured a group of young Irish people travelling around Spain.