The dealership, in Great South Rd, is owned by Team McMillan BMW, which has been providing Rolls-Royce owners with service and workshop facilities for seven years.
Director Bob McMillan said market research had been done to ensure the showroom would be viable.
The Ghost and Phantom Rolls-Royce models would be on display.
Customers will be able to order cars - configured to their personal preferences using colour, wood and leather samples - from England.
Nash said Rolls-Royce had a record year last year, selling 3500 cars.
Emerging markets are driving the firm's growth, with China now its biggest market, just ahead of the United States.
McMillan said sales staff would not be sitting in the Newmarket showroom waiting for prospective customers to appear.
"We're purposefully going out and talking to people and showing and providing the product for 24-hour, possibly 48-hour and even longer test drives."
Rolls-Royce Ghost, extended wheel base
Price: $675,000
Engine: 6.6-litre V12 twin turbo producing 563 horsepower
Acceleration: 0-100km/h in five seconds
Top Speed: 250km/h
Fuel consumption: 13.6 litres per 100km