M&B joins Trident's existing agencies - Starcom, JWT, RPM and AKQA - and will now develop new communications ideas for the Trident brand, which launched amid widespread controversy in January this year.
M&B's appointment follows months of speculation that the confectionery brand is planning to review its media out of Starcom.
John Phillipson, the head of marketing for gum and pocket candy at Cadbury, said the appointment would not affect its relationship with Starcom, which will continue to plan and buy media for Trident. "We are not seeking to replace Starcom. It did a brilliant job on the launch," he said.
Trident was forced to rethink its advertising strategy in April, when the Advertising Standards Authority banned its TV ads after hundreds of complaints from viewers over racist stereotyping.
Phillipson said Trident had secured a 12 per cent market-share since launching. "We've had great success with Trident and we are looking to build on that. We've appointed M&B to use its philosophy and thinking to inject new ideas and new ways to engage consumers," he said.