Howlett spent 15 years at the soft drinks giant in various roles, before leaving in 2001 to become a freelance consultant, advising businesses including Kellogg’s Europe, Heineken and Telefonica.
She rejoined Coke last year as country manager for Ireland within the GB&I leadership team.
Jon Woods, general manager of Coca-Cola Great Britain and Ireland said: "Aedamar brings to the role a wealth of marketing experience having held senior roles across many of our brands and has run the business in Ireland.
"She will be real asset to the business and we look forward to her joining the team."
Coca-Cola said that Brittain had left the company after twelve years to "explore new opportunities", and that he would share details of his career plans in due course. Campaign has approached him for comment.