Sadie becomes Vizeum's worldwide business director, in charge of its global clients. Earlier this month, Vizeum picked up the Heinz media planning and buying account for countries in northern Europe and it also handles international clients including Kia cars and Timberland.
Sadie, 35, completes the management triumvirate on the Vizeum worldwide board, where he will work alongside the chief operating officer, Martyn Rattle, and the worldwide chief strategy officer, Malcolm Hunter.
He is a former managing director of MPG's interactive unit, Media Contacts, and the director of innovation in the agency's strategic planning unit, Catalyst. Most recently, he headed the agency's Intel account and was the managing partner in charge of media strategy for MPG in Europe.
According to Rattle, Sadie will work closely with Hunter, who joined Vizeum in November 2003 from the brand consultancy Red Spider.
"We have got a very complementary team - Malcolm brings brand and consumer skills and Simon brings management and media strategy-based knowledge to the board," he said.
Sadie added: "This job will enable me to engage in the commercial aspect of strategy." He will lead all of Vizeum's client teams across its network of 23 offices.
Separately, Vizeum has hired Rupert Millington from MPG as its worldwide head of product development. In this role, he will be in charge of developing consumer insight across the network.