Peter Rex Dansie, 74, died on Monday from natural causes, the South Australia Department for Correctional Services said.
"All deaths in custody are subject to a coronial investigation," a spokesperson said.
Dansie was jailed in 2020 for murdering his 67-year-old wife, Helen, who drowned after her wheelchair fell into a pond in the Adelaide parklands on Easter Sunday, 2017.
The Advertiser reported that Dansie died in hospital after being transferred from his prison cell.
Justice David Lovell had imposed a life sentence with a 25-year non-parole period, finding that Dansie's motives were financial, and his desire to pursue a sexual relationship with a woman in China.
Justice Lovell said the crime was "an evil and despicable act of domestic violence".
"Helen, your loving and devoted wife for over 40 years, had simply become a burden to you," he said.
"This was a chilling, planned murder of a person whose mistake was to trust you."
He lost two appeals against his conviction.
Mrs Dansie's body and her wheelchair were recovered from a pond in Veale Gardens.
Dansie claimed she had suffered an accident and he had jumped in to save her.
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