The agency won the business after a hard-fought pitch against the incumbent agency, Carat, which had held the business for ten years, and Mediaedge:cia.
Carat's loss of Cadbury is a massive blow, bringing its new-business losses to £70 million this year following the departure of Samsung, Abbey National, Pathe and Opodo.
The agency, usually prominent in new-business performance, has won just Legal & General to balance the losses.
Carat's relationship with Cadbury has included working on the £10 million Coronation Street sponsorship, which the agency negotiated in 1996.
The decision to move the UK account came as part of a global process undertaken by the parent company, Cadbury Schweppes.
It decided to hold pitches on a localised basis, looking at all key markets across the US, Europe and Asia.
European Cadbury business was previously split between OMD, Mediaedge:cia and Carat. Cadbury is continuing to review in Europe on a market-by-market basis.
In addition to the £10 million Coronation Street sponsorship, Cadbury spends £20 million on advertising for brands including Boost, 24-7 chewing gum, Creme Eggs, Crunchie and Dairy Milk.
Its biggest spend was behind the Dairy Milk brand and it spent £2 million on a TV campaign to back Boost Guarana.
Bartle Bogle Hegarty, which backed the creation of Starcom Motive as a media specialist, had handled a part of the Cadbury account before it moved to Carat in 1993.
Cadbury Schweppes is currently rolling out a cost-cutting programming called Fuel for Growth that involves shedding 10 per cent of its 55,000 workforce and selling up to one-fifth of its factories.
It said this week that it had "a complex organisational structure for a business our size and a disproportionate cost base". However, it intends to reinvest up to £400 million of the cost savings in increased product innovation and marketing spend.
In early October, it announced that it would close two of Cadbury Trebor Bassett's factories in Manchester and Chesterfield because of the high level of competition in the market. However, its sales of moulded chocolate have risen 18 per cent.
The Cadbury account brings Starcom's total new-business wins this year to £52 million with its largest win before Cadbury being the £7 million Barclaycard business.
Cadbury Trebor Bassett splits its creative account between Publicis and Euro RSCG Wnek Gosper. Euro RSCG creates the Coronation Street idents. TBWA\London worked for the company but resigned the business to work on Mars brands.
Nobody at Cadbury was available to comment as Campaign went to press.
Starcom Motive refused to comment.