McEttrick will report into group customer officer Robin Terrell and will join the business on 18 May.
She takes over from former CMO Matt Atkinson, who has left the company as a result of a restructure of the marketing team.
"Michelle brings a real diversity of expertise and experience to Tesco. Her experience spans working on and leading the rejuvenation of British Airways and Barclays at BBH, to building the world's largest digital food brand, allrecipes.com, and working for agency clients including Coca-Cola and Frito Lay," said group customer officer, Robin Terrell.
"She is a passionate, creative customer champion, and will be a real asset to our business."
Tesco has recently announced a number of changes to its marketing team. In December, Robin Terrell was promoted to head of customer, taking the reins from Jill Easterbook who moved to head up business transformation.
Sherry Crammond, brand marketing director, and David Wood, managing director for health and wellbeing, also left the business last month as part of the restructure.
This week, Tesco announced its worst results in its history with a £6.38bn loss.