Andrew joins Chemistry from Wax Communications, which was previously known as Dynamo, where she was instrumental in winning the integrated Actimel business as well as leading strategy across a range of accounts including Activia, Johnson's Baby and Johnson's Shower and Shave.
Prior to that she established and grew the planning function in Tunbridge Wells-based agency SMP.
At Chemistry, Andrew will focus on the agency's promotional marketing clients, including Premier Foods, and its Hovis, Cadbury Cakes and Cauldron Foods brands; and SCA Hygiene brand's Triple Velvet, Quilted Velvet, Charmin and Plenty.
She will also be working on Dove on the relationship marketing programme MyDove and other brand tasks.
Andrew said: "I'm really excited to be joining Chemistry at this point in its growth -- the mix of the people, brands and the dynamic environment is really inspiring."
Omaid Hiwaizi, Chemistry's planning director, said: "In building up the department I've very much looked out for the best talent each of our disciplines.
"Catherine has a rare talent for identifying what makes products fly off the shelves -- she'll be a real asset as clients further increase their spend in promotional marketing."