The company, which previously led the scheme through its planning and design stages, will now undertake the improvement works needed to create a safer, more convenient interchange between the station platforms and Gatwick International Airport.
Work is expected to begin in early 2020 and be completed during 2022.
Gatwick airport is the UK’s second busiest airport with the rail station one of the 10 busiest stations in the UK outside of London, handling in excess of 20 million passengers annually.
The redevelopment works will provide crucial increased capacity to support airport growth and a significantly enhanced passenger experience.
Costain Chief Executive Officer Alex Vaughan commented: “The development at Gatwick will transform the existing station and provide a greatly enhanced experience for airport passengers.
“Costain’s extensive capability to deliver complex programmes, using leading edge smart technology, will ensure travellers are kept moving at every stage of the works, minimising disruption during this capacity-critical redevelopment.”