McDade joins from Deloitte Digital, where she has served as group experience director across the consultancy's studios in the US and India.
Swedish creative agency has been re-formed as a 'consultancy' during three years under Deloitte management.
Main succeeds John Seifert, who announced plan to step down in April.
Consumer power has placed online marketing at the centre of business strategy and everyone wants a piece of the action, including major consulting companies.
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