The agency will now be responsible for overseeing a series of campaigns for the organisation over a three-year period, working closely with its creative agency Kindred.
John Ayling's first activity will launch in Spring 2010, and will consist of outdoor, online and press work.
The Milk Marketing Forum is a consortium of British dairy companies and co-operatives, administered by Dairy UK.
The Forum's members include Arla Foods UK, Dairy Crest, First Milk, Milk Link and Robert Wiseman Dairies.
The win for John Ayling continues an active start to the year for John Ayling's business team, and comes a month after the agency picked up new business for Save the Children and Norfolkline.