Greg Turzynski will become the sole managing director following the resignation of his fellow joint managing director, Tim Greatrex (Campaign, last week).
Gerry Boyle, currently the head of planning, Mark Waugh and Tom George, formerly managing partners, have all been made deputy managing directors.
The agency is also reorganising its core business into three client planning business groups. Turzynski, Boyle and Waugh will manage the groups and be responsible for planning leadership, client account management and business development.
George will head up ZenithOptimedia's buying function. This comprises Chris Hayward as the head of television; Jim Freeman, the head of press and radio, and Anna Frith, the managing director of the agency's outdoor arm, Meridian.
Greg Grimmer has been promoted from managing partner to commercial director, responsible for business and brand development.
Jeff Hyams will be the managing director of Zed, the agency's specialist direct and digital agency.
Young said: "This management reorganisation will drive ZenithOptimedia to be more client-centric. These changes, in addition to the adoption of the 'ROI agency' proposition, are part of our strategy to drive a more business-led approach for our clients and increase our focus to improve marketing productivity for advertisers."