The 35-year-old man was taken to hospital with severe bite injuries, but shortly afterwards, local police announced that he had died.
The shark is believed to have been about 4.5 metres long, according to the Australian public broadcaster.
The attack occurred while the man was spearfishing with his family at Michaelmas Island, which is located off Albany in southwestern Australia.
It is the fourth fatal shark attack in Australia this year. The most recent was two weeks ago, when a man was killed by a shark in Queensland.
