The move forms part of a restructure of the agency's senior management team following the merger with Leith last year, which resulted in a number of senior positions being duplicated.
Paul Jeffrey, the planning director, will replace Smith as the managing partner.
Gary Robinson and Owen Lee, former Campaign "Faces to Watch" and creative directors at Farm before the merger, will become joint creative directors and will be in control of all the creative output for the agency.
John Messum, who was also a creative director, will now become the group head of art, with a brief to improve the creative product.
At the same time, Alison Ashworth, the joint head of planning, is leaving to join Euro RSCG London as a planner. Farm is in the process of hiring a replacement.
The restructure also allows John Rowley, the chairman of Leith Edinburgh and Farm, to take less responsibility for the UK agencies in order to focus on a network-based managing partner role with their parent company, Cello.
The changes will also help the agency deal with a number of new account wins, including five from COI, the most recent being the Food Standards Agency's food-safety account in October.