The road is being transformed between Perth and Inverness and Scottish Transport Minister Keith Brown announced the contract to upgrade a second of three stages had been awarded to Jacobs. The US firm took over Scottish engineering company Babtie Group in 2004 and employs some 1,000 staff in Scotland.
The contract, worth between £40m to £60m, will see the section between Pass of Birnam and Glen Garry dualled. Work should begin next month.
Mr Brown said: "This is another step forward for this mammoth project, and underlines our determination to bring forward benefits to road users as soon as we can.
"This multi-million pound investment also complements other work being progressed on the ground to improve the safety and performance of the A9."
Mr Brown said this included the installation of average speed cameras, which would come into effect in October and ground investigation work on the Kincraig-Dalraddy scheme, which is expected to begin construction in 2015/16.
Colorado-based CH2MHill and Glasgow firm Fairhurst won the first design contract, for the 27-mile Glen Garry to Dalraddy section.
The third and final contract, for Dalraddy-Inverness, is due to be awarded by the end of the year.
In all, about 80 miles of road is being upgraded and Mr Brown said the work was on schedule to be completed by 2025.