Seiler will leave his current position as UM chief executive with immediate effect to take on his new role.
He joined IPG as global chief executive of Universal McCann in August 2008, when the group created the Mediabrands structure to house Initiative and Universal McCann.
Seiler will be replaced by Jacki Kelley, who steps up from her current post as UM’s North American chief executive. Kelley joined UM in 2009 from Martha Stewart Living Omnimedia Inc. where she had worked as executive vice-president of media sales.
Seiler’s appointment fills a vacancy that was created in January last year, when Nick Brien was promoted to replace John Dooner as chief executive of McCann Worldgroup.
At the time, it was announced that a new chief executive would not be put in place until 2011.
Brien’s role at Mediabrands was filled by a temporary management structure led by Seiler and supported by Mediabrand Ventures chief executive Matt Freeman, Initiative's global chief executive Richard Beaven, and Tara Comonte, the chief operating officer of Mediabrands.
Michael Roth, Interpublic’s chairman and chief executive, said: "We’re confident Matt and Jacki, joined by Initiative CEO Richard Beaven and Mediabrands Ventures chief executive Matt Freeman, give us the strongest team of media leaders in the business."
Seiler said: "I’m very energized by this new challenge and look forward to building on the great accomplishments of our organisation these past few years."
Prior to joining UM, Seiler served as president and later chief executive of PHD North America, which he joined in 2004.