Edmonds, who is currently a strategy director at the agency, will take on the role immediately and report to the executive planning director, Matt Willifer.
In her new post, Edmonds will be responsible for the day-to-day running of the 17-strong planning department, overseeing its brand, social media and communications planners.
Willifer will now focus on wider management responsibilities, new business and recruitment, as the agency looks to expand its planning team.
Edmonds joined WCRS in December 2010, working on accounts including Bupa and Sky. She has more than 19 years' experience, including seven years in New Zealand before moving to London. Edmonds has also worked at Saatchi & Saatchi, DDB and Fallon.
While at DDB, Edmonds won an IPA Effectiveness gold for the launch of the premium milk brand Cravendale into a commodity market.
Willifer said: "Elisa has been a star strategist for us, and she has also been superb at nurturing our junior talent. I know she'll be great in this new role."
Willifer, a former executive planning director at M&C Saatchi, joined WCRS in September last year. He replaced Jonathan Moore, the former Unilever global brand vice-president, who left the agency in June.