Hedger, who was the global chief strategy officer at Leo Burnett, will join FCB Inferno in April and report to the chief executive, Frazer Gibney.
In addition, Hedger will take a global role within the FCB network.
Hedger replaces Simon White, who is moving to FCB West, the network’s San Francisco office, where he will be the chief strategy officer and handle brands including Levi’s and Electronic Arts.
Hedger worked at Leo Burnett for seven years. He was the group managing director and chief strategy officer until 2012, when he was promoted to global chief strategy officer. He later took back responsibility for the UK strategy operations.
Gibney said: "We’re thrilled to have Giles joining the team at FCB Inferno. He is a truly world-class talent and an intellectual heavyweight, but he wears it lightly. He is a charismatic and charming leader with an infectious enthusiasm and passion for our industry.
"Simon has played a crucial role in FCB Inferno’s success and we wish him all the best with his move and look forward to working with him again on global projects."