The company behind Eastern Western Motor Group runs 29 outlets across Scotland and the North East of England, representing brands including Mercedes Benz, Lexus, Volkswagen and Harley-Davidson.
Profit before tax rocketed from £776,000 to more than £6 million in 2013, as spending on the dealership network in prior years paid off, accounts filed at Companies House showed.
New and used car sales at Eastern rose 13.5 per cent on the prior year, meaning the company fared better than the overall car market.
The Society for Motor Manufacturers and Traders, which will release registration figures for July today, reported that new car sales increased 10.8 per cent in 2013, while used car sales rose 0.9 per cent.
Eastern's five new franchises performed well in the year and "have started to add a meaningful profit contribution".
The firm said its pace of growth has more than offset the demise of Saab, whose UK business fell into administration in 2011.
Eastern's new Volkswagen dealership at the Luxury Car Village at Newbridge, in Edinburgh, is on track to open to the public in October.
The launch will give the firm a "much needed increase in aftersales capacity" alongside its existing franchises at the site.
For 2013, Eastern posted a 6.5 per cent rise in revenues for aftersales, which typically deliver higher margins than car sales.
As well as investment in floorspace during the year, the firm took on an extra 30 staff, taking its total headcount to 948.
The firm has pledged to divert some of its marketing budget towards online sales as it tries to attract the growing number of drivers browsing for and buying a new car over the internet.
Eastern has also set its sights on winning more corporate accounts this year following several successes in 2013, and is exploring ways to offer more environmentally-friendly vehicles as they come to market.
To support its plans to grow, Eastern has agreed a new debt facility with HSBC in July that lasts until 2019. The company sold off property worth £1.85 million during the year, taking the overall value of its real estate holdings down to £37.5 million.
The firm's directors said they were "very pleased" with the company's performance in 2014 so far, though they cautioned that Eastern continued to operate in a "challenging" business environment.
Eastern Holdings is owned and run by Douglas Brown, whose father John founded the company in Edinburgh in 1927.
The company paid an interim dividend of £1 million during the year, doubling the amount it paid out in 2012.
The Society of Motor Manufacturers and Traders has forecast national new car sales of 2.403 million this year, a rise of about 6 per cent on 2013.
However, its predictions depend heavily on the success of the new 64 registration plates that will be released on September 1.