A consortium led by Vinci subsidiary Eurovia and also including local companies Stutz and Rhode will take about three and a half years to complete the works.
The contract involves a €441m (£374m) investment to replace a 29.2km section of the A7 motorway with three new lanes in each direction and operate a 60km section between the Bockenem and Göttingen interchanges. It will come into effect on 1 May.
The financial arrangement follows the decision in February by the federal government, represented by the Lower Saxony authorities, to award the project to a consortium led by Vinci Concessions and also including Meridiam Infrastructure.
The European Investment Bank, CaixaBank, Development Bank of Japan (DBJ), DZ Bank and KfW Ipex-Bank have underwritten the debt for the project, and the arrangement includes a €126m grant from the federal government.
Work will be carried out under the A-Modell, a German contractual framework for financing the renovation and widening of existing motorways and construction of new sections under concessions to the private sector.