Platt-Higgins joined the agency last week as an associate charged with leading its employee engagement practice.
Fishburn's clients in this area include Unilever, Birds Eye, Network Rail and the Department for Business Innovation and Skills.
Platt-Higgins was at Unilever for three years as a global comms director, leading on employee engagement. Before this he headed the planning team at employment comms agency Barkers.
He is a former client of Fishburn CEO Ali Gee from when she was at Edelman.