She formed the agency with Georgiadis, after she left her chief executive role at Zenith Media Services.
Walker's departure will trigger speculation about the future of the agency. M&C Saatchi owns 75% of Walker Media and chief executive David Kershaw recently aired his intention to buy the remaining 25% held by management.
At the end of June Walker will hand over the leadership of the agency to Georgiadis. She will also sell her remaining 14% stake in the agency to M&C Saatchi, which currently owns 75%.
Walker, who said she was leaving the agency "in great shape", intends to take some time out abroad before returning to the UK to pursue other interests. She will remain a shareholder in M&C Saatchi.
Georgiadis said: "I have learnt an enormous amount from Christine and over nearly a decade we have enjoyed a very fruitful partnership. I will, of course, miss her but I am also incredibly excited about the company's future and my role within it."
Walker Media was valued at £18m in 2004 when M&C Saatchi increased its stake from 46% to 75%. Walker netted £3m and was set to get another £3m after two years, and partner Georgiadias received £1.5m.
It is now the eighth largest media agency in the UK and has annual billings in excess of £300m.
Earlier in her career, Walker was part of the 1988 launch of Zenith Media Services out of the Saatchi & Saatchi media department under John Perriss. It was one of the defining moments in the evolution of media planning and buying out of a back office function of creative agencies.
Walker also worked at one of the prototype media agencies Ray Morgan & Partners, which was launched as a breakaway from creative shop Benton & Bowles in 1985.Ray Morgan & Partners was independent from 1985 to 1988 when it became one of the founding agencies involved in the birth of Zenith Media Services.