The Early Contractor Scheme is one of 14 Highways Agency major roads projects which escaped the Spending Review axe.
All 14 jobs, including the A556, are set to start on site by 2015 and a construction timetable for the projects will be confirmed later this year.
The scheme will see the A556 between Knutsford and Bowdon in Cheshire upgraded to dual carriageway standard.
A bypass will take traffic away from the communities of Bucklow Hill, Mere and Over Tabley and Junction 7 of the M56 will be upgraded.
Costain fought-off competition from Balfour Beatty, Interserve, Laing O’Rourke and Skanska to win the job.
Roads Minister, Mike Penning, said: ”I welcome the award of this ECI contract for the A556 improvements. Working with the contractor from an early stage will mean that the Highways Agency fully benefits from contractor’s expertise in design and development.
“This will help the Agency deliver efficiency savings and meet the commitment to start construction on the scheme by 2015, subject to statutory processes”