Police Scotland say the collision occurred at about 3.30 pm on Saturday on the A712 road just north of Glenamour Farm, Newton Stewart, when a Honda 1300 motorcycle left the roadway.
As a result, the 74-year-old male rider from Lancaster was seriously injured and was flown to the Queen Elizabeth University Hospital in Glasgow by Helimed.
In the early hours of this morning the man succumbed to his injuries and died.
Police Scotland are appealing for witnesses to this crash to come forward and contact them at Newton Stewart on the 101 number if they saw anything which might help with the enquiry into the cause of this road traffic collision.