He was 83-year-old Ian Austin from George Street in the town.
Mr Austin was the driver of a Honda Jazz, which was in collision with another car on the A75 road at its junction with the B6357, at the east junction for Annan.
He was cut free from his car by fire crews and taken to Dumfries Infirmary, but he died there three days later on Wednesday morning.
The smash happened at about 11 am on Sunday and the 69-year-old female driver of the other car, an Audi A1, was also taken to hospital. The woman, from Donegal, injured her leg.
Her passenger, a 58-year-old woman, was also taken to the infirmary and two other passengers received minor injuries.
Investigations into the cause of the collision are ongoing and the Procurator Fiscal has been informed.
Police are appealing for witnesses and Sergeant Leigh McCulloch, of the Road Policing Unit, said: “We are carrying out a full crash investigation into this collision and would ask that anyone who may have witnessed it to get in touch with us at Lockerbie on the 101 number.”