The 45-year-old man was part of a group exploring the wreck of the steamship Rondo in the Sound of Mull when tragedy struck on Saturday.
The man’s two companions suffered from decompression sickness – known as the bends – after ascending quickly to fetch help during the incident.
Police said that the 45-year-old, believed to be from Aberdeenshire, died at the scene while his fellow divers were rushed to hospital by Oban lifeboat.
They had been exploring the wreck of the Rondo, a Norwegian cargo ship that ran aground on rocks in the bay in 1935 while the crew sheltered from a storm.
A police spokeswoman said: “Around 10:25am on Saturday, emergency services, including Oban Coastguard and Lifeboat, received a report that a diver – part of a group – had got into difficulty in the Sound of Mull, near to the wreck of the Rondo.
“The diver, a 45-year-old man, died at the scene. A report will be submitted to the procurator fiscal.
“Two other men were brought safely to shore and were taken to the Lorne and Islands District General Hospital in Oban for treatment. They have since been released.”
Stornoway Coastguard was alerted to the incident at about 10:40am on Saturday and tasked Oban lifeboat to help rescue the divers.
The group had been exploring the Rondo, a 2,363-tonne steamship which grounded in January 1935. The crew had been sheltering from a storm when the vessel broke anchor and ran aground on Dearg Sgeir.
The ship later slipped down the steep reef, giving the impression that it is resting almost vertically in the water.
The bow lies in about 50 meters of water, with her stern sitting around nine meters below the surface.
It is a popular wreck for divers and is known for its sea anemones.
Iain Fulton, spokesman for Oban lifeboat, said they had been tasked with getting the diver’s companions to safety.
He said: “We were called to some divers that had got into some difficulty.
“They had surfaced with possible cases of the bends and we had to transfer them back to Oban for treatment.
“It was just off Salen, in the Sound of Mull. The wreck was called the Rondo.”