Frances Ralston-Good has quit as UK chief executive of Omnicom’s Hearts & Science to join rival MediaCom.
It is thought that she will join the WPP agency's global client practice, but a spokesman declined to reveal the exact nature of her new role.
Ralston-Good is returning to MediaCom, where she worked for three years at the start of her career as a planner in the 1990s when the agency was called The Media Business, before it became part of WPP.
She has spent most of the past 20 years at Omnicom, where she won a reputation as one of the leading planners in UK media.
Ralston-Good was named the top media agency planner of the year by Campaign in 2015 when she was chief strategy and innovation officer at Omnicom Media Group.
She went on to be the founding UK chief executive of Hearts & Science in 2016 after its successful US launch as a CRM-focused, data-driven media agency a year earlier.
Expanding the London operation proved slow as Ralston-Good was tasked with integrating the assets of two sister agencies, M2M in 2016 and Rocket in 2018, to beef up Hearts & Science UK.
Notable wins included GoCompare and Betsson Group.
She previously had two stints at Omnicom’s PHD UK, rising to be managing director, and she has also worked at pioneering independent shop Naked Communications in Australia.
Hearts & Science UK chief commercial officer Mark Swansborough and managing director Garrett O’Reilly are to lead the agency following Ralston-Good’s exit. Simon Carr, executive head of planning, is promoted to chief strategy officer.
Philippa Brown, UK chief executive of Omnicom Media Group, said: "Mark, Garrett and Simon have been involved from the start with developing the Hearts & Science proposition in the UK, and given their strong leadership of the agency and close relationships with clients they will ensure that the brand continues to thrive over the coming months and in the future."
Brown is moving to a new role as global chief executive of PHD on 1 July and it is thought that Omnicom Media Group wants to find her replacement before deciding long-term plans for Hearts & Science UK.