The agency's brief is to find ways of connecting the brand with its target audience that go beyond traditional advertising. The Family Brands product is known under various names including Blue Band in The Netherlands, Planta Fin in France and Tulipan in Spain.
M&B's appointment is a reflection of fresh thinking at Unilever that involves trying to put more innovation into its advertising and communications.
Alan Rutherford, Unilever's worldwide head of media, has a brief to introduce innovative companies to parts of the business.
Unilever has not previously worked with M&B but hired the agency after a three-way pitch against Prodio and Lowe's Draft Worldwide. Lowe handles above-the-line creative and Initiative Media handles media.
The agency will work on non-broadcast media across ten markets. Family Brands does not exist in the UK, but is Unilever's fourth-largest food brand in Europe with a turnover of £700 million.
M&B will work with other Family Brands agencies in each market and is tasked with finding new ways of reaching consumers in the way that it has with other brands such as Channel 4 and Butterkist. It is using some freelance creative resource on the account.
Unilever is planning to grow the Family Brands product with a series of launches in the next two years. It currently spends £60 million on advertising across Europe.
Petra Zinkweg, the European brand director for Family Brands, said: "M&B impressed us with its creativity, people, experience and ideas. We're looking forward to a long and fruitful relationship with them."