Life will be creating door drop and experiential marketing campaigns for Cravendale after beating Carlson, Hicklin Slade and BD Network to the account.
The other brands Life will work on are Lactofree, a lactose-free milk alternative, and Café Met, a chilled coffee drink.
The Birmingham-based agency was founded earlier this year by David Poole and Ian Humphris, both ex-managing directors of global agency The Marketing Store, the agency best known for its work on McDonald's.
Louise Barton, Cravendale group brand manager, said she had been impressed with Life: "Having worked with Ian Humphris in a previous 'life' and meeting the new team at Life, we were very excited with their experience and ambition to make Life a success."
The agency's other clients include Mars and Chicago Pizza, both of which were clients of The Marketing Store.
Life offers brand design, promotional marketing and retail marketing as well as DM.
Cravendale invests heavily in promoting its branded milk, with ad campaigns by Wieden & Kennedy London.However, it faces increased competition from supermarket own-brand milk, with Asda and Tesco launching a price-cutting war this week in a bid to win price-conscious customers.