Day, a Brit who has served as GroupM's CFO for the since 2003, becomes COO, a new position at the WPP unit reporting directly to CEO Irwin Gotlieb.
His appointment, Gotlieb said in a statement, recognizes, "the need for a deeper management structure at GroupM," the largest of any of Madison Avenue's corporate-level media management units.
Representing more than $40 billion in worldwide media buys for its clients, GroupM oversees four distinct media services networks - MindShare, Mediaedge:cia, MediaCom, and Maxus - and Gotlieb has indicated in the past that it is more likely to expand its number than to consolidate them. In addition to day-to-day management oversight, Day will be work with WPP to develop new businesses, acquisitions and joint ventures.
Based in New York, Day originally joined WPP in 1988 to work on acquisitions and investor relations, and was a key member of the original management team that launched MindShare globally.
His appointment signals a very different direction for GroupM than its previous top management structure, which had Mandel reporting to Gotlieb in more of strategic role. Before leaving to join VNU (now the Nielsen Co.) as CEO of NielsenConnect, Mandel's title at GroupM was chief of strategic solutions.