Moody will take control of the day-to-day running of the agency's planning department, working with Anthony Edwards, the director of channel strategy who joined from Mindshare in June last year.
She replaces Alison Ashworth, who has left the agency to pursue other interests.
Moody has been at Euro RSCG since 2008, and was recently responsible for leading the planning on the agency's successful Dulux pitch.
She began her career at Lowe, before moving to Duckworth Finn Grubb Waters to head its Co-op account.
In 2000, Moody moved to Abbott Mead Vickers BBDO, where she worked on accounts including the BBC, Yellow Pages and PepsiCo.
She was also the planner on the Sainsbury's campaigns starring Jamie Oliver, which took silver at the IPA Effectiveness Awards in 2002.
Russ Lidstone, the Euro RSCG London chief executive, said: "Given the importance of strategy and planning to an agency headed by a former planner, it is critical to have a top strategist leading the team, and Rebecca is an excellent thinker and brilliant around the creative work."
In April, Euro RSCG bolstered its planning offering with the appointments of Samantha Alonso from Naked Communications and Dare's Rachel Filer as senior planners.