In addition to overseeing the London agency, Haworth will provide creative leadership of the Rapp Collins network across Europe.
Haworth will hand over the day-to-day running of the London agency's creative department to the creative partners Nick Platt and Barney Cockerill, who have been made joint creative directors.
The changes follow last week's news that Marco Scognamiglio has been promoted to chief executive from managing director of the London agency.
The move was designed to free up Chris Gordon, the chairman and chief executive of the WWAV Rapp Collins Group, to devote more time to building the Rapp Collins network in Europe.
Scognamiglio said: "Ian is an inspirational leader. As chairman he will bring a drive and dynamism to the business and ensure that creativity continues to be at the very heart of the agency."
At the same time, Martin Norrie, who was a creative partner of WWAV London, has been named as the creative director at Rapp Collins Consumer Health, the recently launched healthcare unit.