Thorpe-Woods was previously the director of planning at Leagas Delaney, and will be replaced internally by Tony Quinn, who has led planning on key accounts and was due to leave the agency for a job as a senior planner at Ogilvy & Mather.
At Saatchis, Thorpe-Woods fills the position left vacant when the planning director, Kevin Dundas, became the managing director of the Charlotte Street agency.
Thorpe-Woods will head a 20-strong team of planners and will work across all existing accounts as well as marketing the agency to new clients.
He will be coached to eventually take over from Dundas on the network's worldwide planning board.
Dundas said Thorpe-Woods was a crucial addition to the agency since his own promotion to managing director. "We need an experienced manager with serious brand credentials to set the strategic tenor for the department. But just as importantly, we wanted someone with a proven track record on highly creative accounts, and Jeremy's experience will stand him in good stead for his future here.
"His timing is perfect, as our creative product just keeps getting better and better. His job is to fuel the fire, he said.
Thorpe-Woods spent two years at Leagas Delaney, working on Adidas, having joined in 2000 from Abbott Mead Vickers BBDO, where he worked on Guinness and Dulux.
Leagas Delaney's Quinn has been at the agency for four years and will work alongside the managing director, Justin Bairamian, and the joint creative directors, Rob Burleigh and David Beverley.