Costain will widen an 8.7-mile stretch between Chiverton Cross and Carland Cross from a single carriageway to a dual carriageway.
It is the only remaining stretch of single carriageway on the A30 between Camborne and the M5 at Exeter.
The project includes construction of new grade-separated junctions, slip roads and bridges.
Detailed design will start in April 2020 with site works following on in the coming months. The new upgrade is expected to be open for traffic by the end of 2023.
Costain won the contract despite Galliford Try Infrastructure and Vinci being Highways England’s ‘delivery integration partners’ for contracts over £100m in the southwest.