The other two were being treated for hypothermia after being missing overnight on the Southern Uplands.
Bobby Thomson, 64, George Crosbie, 73, and 74-year-old Jeffrey Stewart had failed to return from a walk in the hills at Durisdeer on Tuesday.
The men were found on Wednesday afternoon and taken by helicopter to Dumfries and Galloway Royal Infirmary.
The walkers, who are said to be regular visitors to the Lowther Hills area of the Southern Uplands, left home at 08:30 on Tuesday for a trek and had been due to return at 15:30.
Police said the men were "experienced hillwalkers familiar with the area".
A post on the Moffat Mountain Rescue team's Facebook page described weather conditions in the area as "very wet and windy with very little visibility".
Driving rain and very high winds had hampered the search overnight in the area north of Thornhill in Dumfries and Galloway.
At its height the search involved police, four mountain rescue teams, the search and rescue dog association and a Coastguard helicopter from Prestwick.
Its crew spotted the three men in open ground about 4km from Durisdeer just after 13:00.
The men were airlifted to hospital where one has since been pronounced dead.
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One of the three hillwalkers in their 60s and 70s rescued in Dumfries and Galloway has died, police have said.