Aston Martin has bought the land in Wales for its new factory, which will create 750 new jobs.
The British manufacturer announced in February that it had chosen St Athan as the site of the new facility where it will build its new DBX crossover vehicle.
With contracts exchanged on the land, Aston Martin says it can now begin the first phase of the factory's construction, which includes the reception areas, administration and management offices and the employee restaurant.
From April 2017, Aston Martin will also have access to the three 'Super Hangars' that are on the land, owned by the Ministry of Defence (MoD).
Aston Martin president and CEO Dr Andy Palmer said: "Since taking the decision to build our first SUV in Wales we have been impressed with the commitment and approach from both the MoD and the Welsh Government in making this project work.
"We continue to work with the Welsh Government in areas like recruitment to ensure we are able to meet our project timescales."
Carwyn Jones, first minister of Wales, said: "We are delighted that Aston Martin has chosen to locate its new manufacturing facility here in Wales.