He assumes his new role on May 1, replacing Andrew Norris, who has moved to MPG Sydney, and reporting directly to managing partners Mark Craze and Marc Mendoza.
Prior to joining MTV Networks, Rotherham was international group director at Initiative.
Mendoza said: "Ian is a great addition to the team. He has high-quality, diverse experience, having worked both media agency and media owner sides of the fence.
"His talents will help ensure MPG continues producing powerful work for its clients that truly cuts through with consumers, and that can then be translated into media markets outside the UK."
Rotherham's appointment follows those of Nylon founding partner Martin Thomas as head of strategy and The Allmond Partnership's Jim McDonald as head of broadcast.
Rotherham said: "There is a strong leadership team in place and there has been a considerable investment in talent. I relish the opportunity to play an integral role in developing the business and furthering the agency's aggressive growth targets."
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