Both sites were previously part of Hiram Walker, one of the largest whisky distilleries in the world, until 2001.
Once producing around 25 million gallons of whisky a year, they have now been vacant for over a decade.
Bilfinger GVA together with joint letting agents DM Hall, were responsible for the sale of the two waterfront properties and Culross Ltd will develop the seven acre site primarily for residential property.
The adjacent five acre site was bought by a retailer to complement ongoing commercial activities in Dumbarton Town Centre.
Stephen Robertson, associate director of Bilfinger GVA’s land and development team, said: “These two adjoining sites at Dumbarton Harbour have been vacant for a number of years after the collapse of the distillery in 2002 and most of the buildings on the sites have already been demolished.
“The larger of the two sites is primarily for residential development whilst the second site will complement the commercial activities elsewhere in the Dumbarton town centre.
“The quick sale of both sites, completed within six months of the receipt of instructions, will now add to other Council initiatives to help kick-start the regeneration of this part of the town including a new Riverside Walkway.”