Banks, 28, joins from Initiative, where she held the same position and ran the agency's innovation department.
ZenithOptimedia has given Banks a wide-ranging role: she will oversee the agency's strategic work, generate creative media ideas and recruit and train new planners.
She will also work closely with the head of research, Frank Harrison, to develop techniques that help demonstrate the agency's ROI proposition.
Gerry Boyle, the managing director of ZenithOptimedia, said: "Lucy is lateral in her approach and very pragmatic: she understands a client's needs and pressures."
Banks worked at Initiative for six-and-a-half years. During her time there, she created a manual for planners to use when generating communication ideas.
She said: "This role offers a real chance to develop a culture of effective creativity."