Haworth takes up the post immediately and will retain his job as chairman of the London agency and creative director of Rapp Collins Europe.
In his new role, he will be charged with strengthening the network's global creative output. He will still spend 50 per cent of his time in London and the rest on his international responsibilities.
Haworth's promotion follows the appointment of Gary Von Kennel in March as the network's first global chief executive. Von Kennel said: "People have been talking about global marketing for many years - often in theory rather than practice. Now it's a reality and we have to ensure we can deliver leading-edge creative marketing solutions. Ian will ensure we have creative consistency across the network - creativity at a level that will deliver outstanding return on investment for our clients."
Meanwhile, Gavin Hilton takes the newly created role of joint planning director. Hilton will share the title with Simon James, who has been promoted from head of data planning. Hilton joins from Proximity London, where he was the planning director, and will concentrate on strategic planning. James will focus on data strategy.
Marco Scognamiglio, the chief executive of WWAV London, said: "Planning has to be at the forefront of our business as we strive for excellence in understanding our clients' customers."