He replaces Jonathan Moore, who left the agency in June, and will form part of the new WCRS management line-up, which also includes the chief executive, Matt Edwards, and the executive creative director, Leon Jaume.
Willifer will oversee the agency's strategic offering, helping to develop its brand planning and social media capabilities.
He began his career in advertising at BMP DDB in 1995, working on the agency's Volkswagen business.
In 2003, Willifer moved to Heresy as its head of planning, before joining M&C Saatchi in an equivalent role in December 2005.
Willifer spent three-and-a-half years at the agency, then left in April 2009 to become the chief executive of the games developer nDreams Unite, which helped brands such as Reebok and Sony create bespoke online games.
He has also been the chairman of the Account Planning Group and, in 2009, edited the Gold Standard book, a compilation of all the gold-winning papers since the APG Awards began.
Willifer said: "Innovative communication requires putting different people together in different ways in order to come up with different ideas, and I think WCRS and Engine have realised this more than anyone."