The agency won the business after a pitch that began in May and was handled directly by Volkswagen.
It marks the first time that the two brands have appointed a dedicated CRM agency.
AnalogFolk won Seat’s digital account in 2009 after a pitch against AKQA, Code Computerlove and Soup. However, the agency is winding down its role with the brand.
Volkswagen Commercial Vehicles has worked with a number of agencies on a project basis.
Its most-recent retained shop was Iris.
Proximity’s victory follows Volkswagen Commercial Vehicles’ appointment of Kirsten Stagg as its head of marketing earlier this year.
Stagg said: "I’m delighted to be working with Proximity as our new CRM agency for Volkswagen Commercial Vehicles. We’re looking forward to introducing CRM to our marketing activity in the UK."
AnalogFolk created an augmented-reality app for Seat that launched in 2013. The app, available for visitors at showrooms, enabled potential customers to discover more about the Seat Leon using Blippar technology.