The man from Kirkgunzeon, four miles from Dalbeattie, was thrown from his machine when it careered out of control on the B793 Dalbeattie - Caulkerbush road at Drumstinchall, three miles south of Dalbeattie.
It is believed to have crashed into a wall near a minor road junction at the top of Drumstinchall hill.
The accident happened late on Sunday night and the man, who has not been named, was treated at the scene by paramedics before being taken 20 miles to Dumfries Infirmary.
He was rushed 80 miles north to the Western General Hospital in Edinburgh for specialist treatment where he was said to be critical after undergoing emergency surgery.
The man was alone on the machine when the accident happened and police said no other vehicle was involved. They are trying to find out when the man was out late on Sunday night on the bike.
A Police Scotland spokesman said; “The man has been undergoing surgery and his condition is critical. We are investigating the crash and a full investigation has been carried out at the scene.”
Police are appealing for witnesses to the one-vehicle crash which took place about 10.15pm on Sunday night. The road was closed throughout the night and was re-opened around 6am this morning.
A spokesman said: “Police are particularly keen to speak to anyone who may seen a quad bike travelling after 8.30pm last night on the A710 Dalbeattie - Dumfries Road or on the B793 Caulkerbush - Dalbeattie Road.”