The site, alongside Sytner-owned Oxford Saab and Guy Salmon Jaguar Oxford, is Johnsons’ second Lexus dealership.
AM understands that Johnsons will relocate the dealership when the lease runs out in two years.
The company has signed a confidentiality contract with Sytner preventing it from talking about the details of the purchase.
Geoffrey Page-Morris, Sytner operations director, said Lexus informed the group two years ago that the site did not conform with its latest franchise standards.
After failing to find another suitable Lexus site in the Oxford area, the manufacturer put Sytner in touch with Johnsons, Page-Morris added.
He said the site was profitable at the time of sale.
Johnsons already owns Lexus Liverpool, as well as 15 other dealerships selling Honda, Toyota, Volvo and Volkswagen, while Sytner has five Lexus dealerships in Birmingham, Bristol, Cardiff, Leicester and Milton Keynes in its chain of 128 outlets.
Lexus is a valuable franchise – it has topped the JD Power customer satisfaction survey for eight consecutive years.