Andrew Mallard was imprisoned for 12 years over the 1994 death of Mosman Park jeweller Pamela Lawrence but had his conviction quashed by the High Court in 2005 and was freed in 2006.
A spokesman for the WA government confirmed to AAP Mr Mallard had been killed on a Los Angeles road.
“I’m terribly saddened by this tragedy,” Attorney-General John Quigley, who led the fight to overturn the conviction, said in a statement on Friday.
“It’s just fortunate that he got to spend 13 years of freedom after so much time wrongfully imprisoned.”
A WA Police spokesman said: “WA Police have been advised of the death of Mr Andrew Mallard in Los Angeles.
“We have notified Mr Mallard’s family in Western Australia and we extend our condolences to them at this difficult time”.
Mr Mallard reportedly had been living in the UK but frequently visited friends in the US.
He was in 2009 given a $3.25 million ex gratia payment for his time behind bars after lengthy negations with the state government.
Mr Mallard had sought $7.5 million.
Police consider Mrs Lawrence’s likely killer was British backpacker Simon Rochford, who committed suicide in an Albany jail in 2006, one week after police interviewed him about the murder.
The initial investigation and Mr Mallard’s wrongful conviction were the subjects of a Corruption and Crime Commission inquiry, following which two assistant police commissioners, Mal Shervill and David Caporn, were forced to step down from their jobs.