The business, which has dealerships selling major car marques in Aberdeen, Dundee, Dunfermline, Edinburgh, Kirkcaldy, Perth and Cupar, has seen pre-tax profits jump 15.8% to £4.4 million during 2012.
The company, which was running 17 dealerships by the end of the period, saw turnover rise 15% to £354m.
This reflected a 20% increase in new vehicles sales to a 8483, and a 17% uplift in used sales to 7079.
And the company, which is focused on the east of Scotland, has seen business continue to motor in 2013, with new registrations powering sales to beyond the 3000 mark in September.
New registration sales at John Clark in September were up 36% on last year, boosted by the acquisition of four dealerships compared with a market average of 12%. Stripping out the effect of the acquisitions, like for like sales were still ahead of the market at 18%.
Chairman and managing director John Clark, who established the business 35 years ago, said: "There is greater consumer confidence, however, the cost of borrowing now is considerably less than it ever was.
"Fuel efficiency of cars is considerably better than it ever was, so in fact, if you can change your existing car for a new car that is better and more fuel-efficient for the same money you are paying per month, that is what is creating the market.
"One aspect is the lower interest rates. The other thing is most manufacturers have become very competitive in their pricing. If you look at the monthly payment you are paying today and the monthly payment you were paying three years ago, it is probably lower pro rata."
Mr Clark said the strength of the Aberdeen economy had boosted sales in the north east, but insisted there was more to his firm's story.
He said: "You have got to remember you can buy a car anywhere. In real terms, yes, we do well in Aberdeen, but we also so well in Edinburgh and Dundee.
"It helps because we have premium-end brands, and the premium brands have actually probably moved downwards in sector an awful lot more.
"A 1 Series BMW is probably the same price as a Ford Focus these days - in real terms it is getting into a greater market."
As well as reporting record car sales, the firm booked best-ever results for its service workshops, accident repair centres and parts operations for the seventh year in a row. The firm now has 21 outlets after taking on two Jaguar and two Land Rover dealerships in 2013.