The project to build a bypass for Maybole could employ up to 165, it has been claimed.
Scottish Government bosses said work on the A77, which will cost £31.5 million, is now ready to proceed.
It follows the official award of a construction contract to Willis Bros Civil Engineering.
The project will create a 3.1-mile (5km) road designed to ease the burden of traffic thundering through the tight confines of Maybole.
Transport Secretary, Michael Matheson, said: "The local community will benefit from opportunities created for small and medium enterprises to bid for subcontractor roles and the provision of at least four vocational and seven professional, site-based training opportunities.
"The contractor anticipates that the project could employ up to 165 people during the months of peak construction activity, a number of which are created by the project.
"We recognise the strategic importance of providing good transport links on the major routes to the key port at Cairnryan.
“Today’s announcement continues to build upon the significant investment already delivered across 10 improvement projects since 2007 on the A77 and A75.
“Delivering the Maybole bypass will provide better journey time reliability for road users as well as improved safety and environmental benefits for the local community."
South of Scotland MSP, Brian Whittle, added: "After so many long years of waiting and so much hard work by local residents and campaigners, I'm delighted to see the Maybole Bypass moving forward.
"The new bypass will benefit drivers on the A77 and opens the way for new investment and redevelopment in Maybole.
"It is disappointing that the Scottish Government chose not to fully dual the bypass, missing an opportunity to futureproof the road, but it’s still a major step forward for the area.
"This is an important investment but there’s much more that could be done to improve the A77 along its entire length.
"Instead of resting on their laurels with this investment, I’ll continue to challenge the Scottish Government to set out a long term plan for further bypasses and more dual carriageway that will bring the A77 up to the standard drivers expect from a trunk road and help grow the economy across Ayrshire."
