The contract is worth £16m a year to Amey and runs for 15 years, making it worth £240m over the full life of the deal. It starts in November 2020.
Amey will manage three major structures: the M5 Avonmouth Bridge spanning 1,400 metres; the M4 Prince of Wales Bridge; and the M48 Severn Bridge
The M4 Prince of Wales Bridge itself comprises of three structures: the Avon viaduct (2,100 metres), the cable stay main span (948 metres) and the Gwent viaduct (2,077 metres).
The M48 Severn Bridge is a 1,600-metre suspension bridge that has the second highest tidal range in the world at 14.5 metres.
Amey will be responsible for the cyclic maintenance, daily structure inspection checks and safety patrols as well as responding to any incidents that impact the structural integrity of the bridges that make up the Avonmouth and Severn Bridges contract.
Highways England operations director Nick Harris said: “Our roads and bridges are among the safest in the world and partnerships like this will help maintain high standards on the three large bridges in the southwest. By working more closely with our supply chain who carry out maintenance, we will be able to work more effectively, identify innovative ways of working and provide the best possible quality of service to road users.”