Mullins joins from Laing O’Rourke where he had responsibility for the delivery of the shell, core and envelope of Heathrow Airport’s £1bn T2 which opened to passengers last month.
Mullins will provide overall leadership across GB’s offices in Sunbury and Rugby.
GB operations director Peter Smyth said: “Steve joins us at an exciting time for GB as we accelerate plans to grow our presence in the central and southern regions.
“He is a passionate supporter of continuous improvement and innovation, and brings with him a detailed knowledge of off-site manufacture, health and safety and client facing delivery.
“Steve is a strong addition to our senior leadership team and will offer a commercially creative approach to new initiatives and problem solving.”