The event will include an afternoon conference for around 350 guests followed by dinner, entertainment and an awards ceremony.
The aim of the event is to celebrate and recognise the performance of UK dealership personnel.
The event will be branded with its own identity with a dedicated website designed to help and inspire delegates in the build-up.
Claire West, client services director of River Marketing, who was part of the recent management buyout of the Oxfordshire agency, said: "Winning any piece of business is exciting but we’re particularly pleased to be working with BMW Group Financial Services for the first time."
Sophie Grimshaw of BMW Group Financial Services said: "River Marketing has an impressive track record and their proposal for this important event has given us every confidence that they will deliver something very special."