The 35-year-old was bitten by a suspected 4.5-metre shark after 11am on Saturday off Michaelmas Island near Albany in Western Australia's south west.
"He was conveyed back to shore by boat where he was met by paramedics,'' WA Police said in a statement.
"Sadly, he was unable to be revived."
WA Premier Roger Cook said he was "deeply saddened" by the incident.
"This is a tragedy and my thoughts are with the victim's family and friends, as well as the first responders," he said in a Facebook post.
"I know members of the community will wrap their arms around them."
Authorities urged people to take additional caution in the Michaelmas Island area and adhere to beach closures.
The death comes after father of two, Steven "Mattas" Mattaboni, was killed while diving at Horseshoe Reef off Rottnest Island near Perth in May.
The 38-year-old was pulled from the water after being bitten and was rushed by boat to a jetty at Geordie Bay on the north side of the island.
Paramedics were unable to revive him.
A five-metre white shark was spotted 80 metres offshore about the time of that attack, according to Surf Life Saving WA.
Police will prepare a report for the coroner.
Michaelmas Island is about 15 kilometres from the seaside town of Albany, which is about a five-hour drive from Perth.
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