RJ McLeod (Contractors) have won the A77 Symington to Bogend Toll Improvements scheme and the A75 Dunragit Bypass.
The A77 job is worth £10.6m and will start on site this spring.
McLeod beat-off competition from Farrans, John Paul Construction and South West Highways to land the scheme.
The A75 Dunragit Bypass contract is worth £17.13m and will also start this spring after McLeod beat Balfour Beatty, Carillion and John Graham to the deal.
The third scheme on the A75 at Hardgrove will be carried out by McLaughlin and Harvey where the contractor will deliver a new £9m stretch of road.
McLaughlin & Harvey beat Balfour Beatty Civil Engineering, John Paul Construction, I & H Brown and RJ McLeod to the job.
Transport Minister Keith Brown said: “This significant investment in lifeline routes in south-west Scotland worth in total over £36 million, will be welcome news in local communities, and underlines the Scottish Government’s commitment to improving these essential roads.
“I look forward to construction getting under way very soon so that road users can begin to feel the significant benefits the schemes will bring.”