The Douglas Park Mini and BMW site, on Kyle Street in central Glasgow, has seen its floor space more than double to around 5000 square metres, meaning the full footprint of the site is now being utilised.
The year-long project has given the business a significant amount of additional room to display a greater number of cars and Cameron Wade, dealer principal, said the dealership is now "a much more retail-focused environment".
The changes include consultation rooms for customers and staff, a coffee bar, a play area for children and an internet zone where people can go online.
There are also interactive visual displays where customers can build their own vehicles in a range of specifications and colours.
As a result of the investment, an additional 12 staff have already been taken on with the company, which employs around 40 staff at the site, signalling it could potentially add more people in the coming months.
Mr Wade said early feedback on the changes from customers had been "very, very positive".
The site was officially opened at an event last night attended by BMW's UK managing director Tim Abbott.
The latest investment comes on top of the £3.5m Park's Motor Group spent on an aftersales centre in Glasgow during 2012 and the £1.1m opening of a BMW Motorrad dealership for motorcycles at East Kilbride in June this year.
In recently filed annual accounts, Park's of Hamilton (Holdings), parent of Park's Motor Group, saw its pre-tax profits increase from £10.5m to £12.2m.
Turnover at the motor division of the company rose from £316.8 million to £321.7m in the 12 months to March 31, 2013.