She replaces Olga Martinez Garcia, who was recently appointed to the role of marketing and innovation director, Latin America and the Caribbean.
Miles joined Diageo from Reuters in 2002 as strategy director. She then spent time in a number of marketing and innovation roles in the GB and Europe businesses, leading brands such as Smirnoff and Captain Morgan.
Miles has recently returned from two years in Mumbai as marketing services director, Asia Pacific, and has been working as global brand director, Bushmills since May.
She starts her new role immediately and reports into Diageo managing director Simon Litherland, who said: "I am confident that Sarah will continue the growth of Reserve Brands."