According to the agency, a new MD of Cohn & Wolfe UK Consumer Marketing has already been appointed to succeed Grant and will join in March.
Grant will however retain her role as head of Cohn & Wolfe Consumer Marketing EMEA, and will continue to report to Scott Wilson, UK CEO and managing director, EMEA.
Wilson said: "Our UK Consumer Marketing business has been on fire, with revenue tripling over the past four years. During this period, Rebecca has been at the forefront of driving our wider agency transformation, and much of our success has been founded on a commitment to placing collaboration, creativity and digital at the heart of everything we do."
Grant joined Cohn & Wolfe from Weber Shandwick in 2011, where she was a senior director and head of the European brands practice. She began her PR career at Red Consultancy, working on clients including Nokia, Amazon and Singapore Tourism.
A statement announcing Grant's appointment said in 2015 Cohn & Wolfe UK had its fifth consecutive year of double-digit growth.