Before taking up the role he chaired a number of well-known businesses including the European arm of Cott Beverages and dried fruit company Whitworth's. Prior to this, Mustoe held European and UK executive roles within the Campbell's Soup Company
Mustoe told First Milk members of his decision in a letter this week.
‘Pass on the baton’
"Throughout my career I've learned that there's always a right time to pass on the baton," said Mustoe. "None of us are getting any younger and I've just turned 70, so with a settled management team and a clear strategy in place, October just seems the most appropriate time."
The group said it is currently searching for a replacement for Mostoe.
In addition, Mustoe confirmed the appointment of Pembrokeshire farmer and board member Nigel Evans to the role of vice chairman designate in place of Tom Campbell. Campbell will also leave in October.