It is believed to be the first time the brand has appointed one agency across all parts of its business.
Cohn& Wolfe will work across all Ferrero's brands, which include Tic Tac, Ferrero Rocher, Kinder Bueno and Nutella.
It will also handle a corporate reputation programme for the brand and manage an ongoing press office.
The retained account was won following competitive pitch. It is believed that Grayling and Lexis PR also pitched for the account.
Cohn & Wolfe will report into marketing director Dave Tucker.
'This win demonstrates that within the agency we have the breadth and depth of experience in the food and drink sector that can cover all of a company's needs from corporate reputation to high impact consumer campaigns', said deputy MD Caroline Maddock.