Thomassen's appointment follows the departure of Campbell's UK strategic planning manager Steve Morris last year. Morris is taking a career break.
Thomassen joins the company from PepsiCo Beverages International, where she was customer and channel insights manager for Europe, based in the UK.
During her four years at the soft-drinks giant, she was also responsible for implementing in-store programmes. Prior to PepsiCo, she worked for Gillette Sweden as consumer marketing manager.
She starts at Campbell's next month, reporting to marketing director Tim Perman.
Perman said: "Campbell's has nearly doubled its investment in consumer research in the past 12 months and we plan to continue increasing our focus in this area. Debbie will play a key role in helping us identify insights to increase business growth."