Halcrow will carry out preliminary strategic environmental assessment and Jacobs will carry out preliminary engineering work for the major road project which is due to be complete in 2025.
Scottish transport minister Keith Brown said: “This £3bn complex and challenging programme will be one of the biggest infrastructure projects in Scotland’s history.
“We are the first government to commit to a full A9 dualling programme. This commitment will deliver major economic benefits to road users, businesses, communities and industry who live along or use this important lifeline route between central Scotland and the Highlands and Islands.
He said: “The project is further evidence of the Scottish Government’s commitment to supporting the economy by competently delivering major infrastructure projects.”
The work will also examine how the programme may be packaged into individual projects.