The appointment follows a review, which is thought to have included two other agencies, including the incumbent shop, Dentsu Guangzhou.
Starcom's brief will include all of Cadbury's chocolate and non-chocolate brands, including Halls. Cadbury is focused on growing its market share in China, where consumption of chocolate is still relatively low.
Angela Ng, the Starcom Beijing general manager, said: "It definitely wants to increase market share and sales and be more focused in its marketing. Chocolate is still very much a foreign food, but the Chinese consumer's tastebuds are changing."