Ged Parton, CEO of Synovate's brand and communication practice, said that the company was grateful to Callebaut for his contributions and wishes him well in the future.
He said: "Jan's work in adapting psychology to study consumer motivations has provided a solid foundation for the next generation of Synovate Censydiam offerings."
Callebaut will concentrate on Callebaut Delvaux, the strategy consultancy which he founded earlier this year with Willy Delvaux.
Parton added that 140 new Synovate Censydiam researchers have been trained over the past nine months, with many of them based in the fast-growing markets of Asia and Central/Eastern Europe.
Herman Toch, CEO of Synovate Censydiam, said: "Our emphasis is working with our clients to better use research findings in influencing the development and execution of their marketing strategies."
Toch also said that the company's operation in Belgium will continue to play a key global role.
He added: "Our new interactive panels and chat sessions bring the Synovate Censydiam model and thinking into the digital age. These offerings are the first in a suite of integrated online products that will give our clients fresher, quicker insights."