Ms. Gowl headed up the consumer health-care business at Interpublic Group of Cos.' FCB, where Merck & Co. is a significant client.
Ms. Gowl is expected to take a major role in overseeing JWT's business on its global account for Pfizer, which includes brands such as Listerine, Lubriderm and Celebrex.
At JWT, Ms. Gowl will assume some of the responsibilities formerly held by Mary Baglivo, who in addition to her job as chief operating officer also served as an executive on Pfizer.
Ms. Baglivo in October became president of Panoramic Communications.
Ms. Gowl is expected to start at JWT Dec. 10.
A spokeswoman at FCB confirmed the move. A spokesman for JWT would not comment.