Whelan begins his new role immediately and will report to Havas’ global chief executive, David Jones, and its global president, Andrew Bennett.
In addition to working on pitches and special projects across the Havas Group, Whelan will continue to work on social responsibility matters as well as overseeing key Cake projects.
Whelan co-founded the PR company Cake in 1999 and Havas acquired the agency for an estimated £12 million in 2008. Earlier in his career he worked at CDP, Duckworth Finn Grubb Waters, and the media agency BBJ (now Vizeum).
Jones said: "Mark gets two of the most important subjects for Havas and our clients - social media and social responsibility in business and importantly the fact that far from being two separate subjects they are actually intrinsically interlinked.
"He's a huge creative talent and someone who has been doing ‘content’ since before it became an industry buzzword."