Sherman, who joined the agency three years ago, is relocating to Australia and is talking to a number of agencies there about a job.
Starcom Mediavest will not directly replace Sherman, who has worked on strategy and planning across the agency's client base. However, the chief executive, Iain Jacob, has beefed up the agency's planning resources in recent months.
Sherman will leave at the end of July.
Sherman spent eight years at M&C Saatchi and Walker Media before joining Starcom Mediavest. He was the media director at M&C Saatchi before moving to Walker as a managing partner.
Early in his career, Sherman worked in Bartle Bogle Hegarty's media department with Jacob and Mark Cranmer, who is now Starcom Group's chief executive for Europe, the Middle East and Africa. Sherman said: "I'm going to Australia. It is a life-change decision and I am happy to be leaving at a time when Starcom is so strong."