Moore has returned to Ireland and will start at McCann Erickson Dublin next week as a planning director.
The departure will come as a blow to AnalogFolk, which opened its doors in February, promising a "creative co-operative" that would build "communication products" for clients using traditional and digital forms of media.
Moore, who will not be replaced, joined the start-up in December as its third partner. His remit was to head up a media division, using his client background to look at new ways of negotiating client contracts. His responsibilities will be assumed by the remaining partners.
Before joining AnalogFolk, Moore had been at Diageo since 2001, most recently as a media manager, where he oversaw individual agency relationships across the UK and Ireland.
Before that, Moore worked in the company's procurement department and was previously the group sales manager of the Irish broadcaster, RTE.
The other five partners remain in place. They are: Bill Brock and Matt Dyke, the former managing director of Tribal DDB and the planning director of DDB respectively; Ed Ling, the former i-level strategy director; Matt Hardisty, the former global creative director at Naked; and Deirdre McGlashan, the former network director of Isobar global.
A spokesman for AnalogFolk confirmed that Moore had left the agency and would not be replaced. Moore could not be reached for comment.