The move follows a commercial review at Vodafone, and it's understood there was no pitch involved in the process.
Louise Kuegler, the head of brand and insights at Vodafone, said the timing was right for a change given the transformation the business is currently undergoing.
FCB has over the years developed a number of popular campaigns for Vodafone. Some of the more notable work included the use of actor James Rolleston as the face of the brand, while another endearing campaign featured the story of a lost piglet named Piggy-Sue.
The Piggy-Sue campaign proved so likeable that the Irish arm of Vodafone decided to replicate the campaign for its market.
Vodafone spent more than $45 million on advertising this year, according to Nielsen media spend figures.
Losing a client of this magnitude will come as a tough blow to FCB, particularly given that it comes so close to the Christmas break.
A source with decades of experience in the advertising business told the Herald this was likely the biggest account move of the year and that a client of this size would normally be serviced by a team of at least 15 staff. However, the source added that the agency may be able to mitigate some of the losses by moving staff internally or if it was able to win some new business.
FCB wouldn't comment on the number of people working on the account nor the number of job losses likely to result from the change, but a statement from the agency said it had recently won three yet-to-be announced client wins. At this stage, it is unclear how big these accounts are in comparison to Vodafone.
FCB global vice chairman Bryan Crawford expressed disappointment at not being able to work with the new Vodafone management team, led by new chief executive Jason Paris.
"I couldn't be prouder of the unwavering professionalism, commitment and resilience of the FCB team during our tenure," Crawford said.
"I know our team at FCB will show the same level of commitment to Vodafone until the business transitions, probably around the first quarter 2019."
This comes off the back of a tough year for FCB, with the agency confirming a round of redundancies earlier this year and also parting ways with former CEO Dan Martin.
FCB also said it would shortly announce a replacement for Martin.
There is also a sweet and sour element to the win for DDB in that the agency will now have to part ways with its telco client, 2degrees, which the agency has held since winning the account in September last year.
DDB chief executive Justin Mowday said he couldn't resist the opportunity to work with Vodafone and thus reluctantly had to part ways with 2degrees, which is yet to announce a replacement agency.
The arrival of a telco on the market will no doubt spark the interest from a number of agency suitors in this market.
The Herald is yet to receive comment from 2degrees.
