The move comes in the wake of a hostile takeover bid by Kraft, which is understood to have put Cadbury under pressure to analyse its cost base.
The realignment means an end to Cadbury's four-year relationship with The Furnace.
Meanwhile, George Patterson Y&R Melbourne will add Boost to its existing work, which includes Picnic and Cherry Ripe. Saatchi & Saatchi Sydney will continue handling the Dairy Milk portfolio, while Publicis Mojo oversees Freddo, Roses and Cadbury's innovation work.