The group will shortly be transferring its Toyota franchise from Tottenhill to the former Inchcape site on the Hardwick Industrial Estate.
The Ford site - until now held by EMG in Beveridge Way - will be launched there at the beginning of September.
Marshall said that a new team would be recruited to represent Ford in the next few weeks. It is also taking over the Ford commercial franchises in Cambridge and Bury St Edmunds in September.
Marshall's chief executive Roger Knight, says: "These new territories fit in well with our existing businesses and we look forward to strengthening our retail and business operations with the addition of this franchise."
Marshall has been in West Norfolk since 2003, when it took over the Toyota franchise occupying showrooms and workshops beside the A10 at Tottenhill.
The new site has been empty since Inchcape closed earlier this year at the time of the MG Rover shutdown.