The UK incumbent is PHD but the Omnicom agency decided not to repitch for the account when the review kicked off earlier this year.
Carat has picked up the US media planning and buying work from Publicis Groupe’s MediaVest. Carat will also work with the Cadbury-owner in Asia-Pacific.
The Starcom Mediavest Group network has retained Mondelez’s Eastern Europe, Middle East and Africa region and Latin America.
Bonin Bough, the chief media and e-commerce officer, said: "Centralising our media buying with Aegis and SMG offers us a significant opportunity to drive enterprise-level efficiencies that can be re-invested in our long-term growth.
"It also enables us to build our capabilities in key areas of our growth strategy, like e-commerce, content monetization and data-driven insights."