Waite will join the independent agency in the new role at the end of May and sit on the management board with its co-founders Paul Houlding, Steve Hastings, Rob Fletcher, David Alexander and Sue Laing.
Waite will oversee the day-to-day running of the agency and reports to the chief executive, Houlding. She joins from The Red Brick Road, where she had worked since 2007 on accounts including Tesco Bank and Thinkbox.
Houlding said: "Barbara brings with her an exceptional track record and is the ideal person to build on what has been an exceptional period of growth for the agency."
Last year, Isobel won the integrated account for The Bordeaux Wine Council, the body that represents the region's wine growers. Other Isobel clients include Bernard Matthews, Diageo, Kettle Foods and Blossom Hill.