Working alongside Lee Daley, Saatchis' new chief executive, Stanners is briefed to develop the agency's role as more than a traditional TV and print advertising shop.
Heading a department of 20 creative teams, Stanners is also expected to improve creative output across Saatchis' portfolio, which includes Procter & Gamble, Carlsberg and Toyota.
Replacing Tony Granger, who is returning to Saatchis' New York office at the start of next year, Stanners will take up her new role in January.
In addition, Daley has introduced a second-level management tier at the agency, promoting John Wright, the director on Toyota and Ariel, as its managing director.
Two further promotions see Peter Lovatt, the former director of Carlsberg UK, become the director of professional services, and James Griffiths, who ran the NSPCC, become the agency's new director of orchestration and innovation.
Most recently, Stanners co-founded Boymeetsgirl, leaving the agency in September, following a dispute with the partner Andy Law. Before this, she was the executive creative director at St Luke's.
Stanners started her career as an art director at GGT in 1988. Six years later, she joined Bates, where she began a 12-year collaboration with the copywriter Tim Hearn, creating ads including the famous Flake spot featuring a girl in the bath.
Bob Isherwood, Saatchis' worldwide creative director, said: "Kate's all the things you would want in a creative director. What put her on top of my list, though, is she is an ideas person."