It follows a pitch against Abbott Mead Vickers BBDO, Bartle Bogle Hegarty, WCRS and the incumbent, BMB.
Adam & Eve/DDB and WCRS were then selected to take part in a final shoot-out earlier this week.
Agencies were told the news on Wednesday morning. The frozen-food manufacturer called the pitch in July in a process handled by Roth Observatory.
The appointment marks the end of an 11-year relationship between McCain and Trevor Beattie, the co-founder of BMB.
Mark Hodge, the marketing director at McCain, said: "From our very first meeting, Adam & Eve/DDB have impressed us with their thinking and ideas. We are looking forward to working with them.
"At the same time, it is also important to acknowledge and thank BMB for the significant contribution they have made to our business over the last eight years."