Mediabrands, owner of the UM and Initiative agency networks, has streamlined its global operations from four divisions into three. Operating units for North America, Europe Middle East and Africa, Latin America and Asia Pacific will be divided into North America, the G14 and "world markets".
Following the changes, Hytner will become president of the G14 for UM, with responsibility for the 14 most strategically important markets outside the US, putting the UK alongside Japan and Australia.
Initiative worldwide chief strategy officer Eric Bader, former president of mobile marketing company BrandInHand until he joined Initiative in 2010, will take the role of president of the G14 for Initiative.
The G14 is estimated to account for around 30% of Mediabrands' revenue and includes Germany, France, Brazil, Russia, India and China alongside the UK, Japan and Australia.
Hytner said: "This is purely a leadership development. The change is that I [and Bader] will be managing the 14 most strategically most important markets, as deemed by our clients and economic studies.
"All our regional teams will continue to work for clients on regional business and will report to me."
Hytner said the restructure followed "three to six months" of research and the G14 were the markets chosen were the ones which were the most likely to "cross pollinate".
All the local UM chief executives in the G14, including the UM London's Andy Jones, will report to Hytner, as will executives that lead regional business, such as Mastercard in Latin America.
North America remains the largest market with around 50% of Mediabrands' revenue. The "world markets" division includes all areas outside of North America and the G14, including South Korea, Hong Kong, Austria and Switzerland.
There will be no job losses as a result of the changes. Tim Spengler will continue as president of North America for Initiative and two candidates are understood to be being considered for the North American UM role.
The restructure is at a global management level and will not affect the work of UM's regional teams, who will continue to work with and pitch for clients regionally.