Buhlmann has been in his current role since 2003. Before that, he was the chief executive of Carat International for three years and has also spent time at Young & Rubicam, WCRS and the media agency BBJ, which was bought by Aegis in 1999.
De Nardis was made the global chief executive, then a newly created position, in October 2005. He joined from Mediaedge:cia, where he was also the global chief executive.
Buhlmann said: "My priorities will be to maintain our record of market-leading growth through continuing expansion in digital and emerging markets, efficient operations, extending our client relationships and ensuring we continue to have the most competitive offer in our market."