The long-awaited roadworks – expected to last a year – will upgrade the notorious bottleneck on the A82 at Pulpit Rock, near Tarbet on loch Lomondside.
Civil engineering firm McLaughlin and Harvey will build almost half a kilometre of new road, including a new viaduct section running parallel to the shoreline.
The road will also be widened to allow vehicles to pass more easily at the beauty spot.
The project, set to begin in autumn of next year, should bring an end to the need for traffic lights at this location over the past 30 years.
Transport Minister Keith Brown said that the works will give Pulpit Rock a road 'befitting its setting and importance'.
He said: "The A82 Pulpit Rock scheme sits within one of the most scenic landscapes in Scotland that brings many visitors to Loch Lomond.
"This project will bring real benefits for businesses and communities in the Highlands and Islands, not least the haulage industry."
The construction of the viaduct and the cutting of roadside rocks will require the A82 to be closed in each direction for up to 14 weeks between October 1 and January 6 2014.
Transport Scotland say traffic flow is lightest during this period and it decided on the time frame following a consultation with the local community. But concerns have previously been raised about the affect this could have on the winter tourism industry.
Other short-term road closures may be required during the work but Transport Scotland said it would work with contractors to keep these to a minimum.
Mr Brown added: "Throughout the procurement process emphasis has been placed on minimising the impact on communities and businesses.
"I have tasked Transport Scotland to ensure this continues to remain a key focus throughout construction."