The works at Pulpit Rock will remove a notorious bottleneck around the famous Loch, getting rid of traffic lights, which have been there for 30 years.
The improvements include a new 400m section of two-lane carriageway, a viaduct running parallel to the loch shore for 180m and the widening of the existing carriageway.
McLaughlin and Harvey will start the project described as a “real engineering challenge” in the spring.
In the last few months the contractor has won several harbour works jobs in Aberdeen, Isle of Skye and Stranraer as well as several supermarket builds.
Transport Minister, Keith Brown said: “The A82 Pulpit Rock scheme sits within one of the most unique and scenic landscapes in Scotland that brings many visitors to Loch Lomond. We fully recognise delivery will not be without its engineering challenges.
“Our commitment to improve the traffic flow at Pulpit Rock is unwavering and, on completion, this project will bring real benefits for businesses and communities in the Highlands and Islands, not least the haulage industry.
“This is why I am pleased the announcement our preferred contractor shows, at long last, Pulpit Rock will have a road befitting its setting and importance.”