Police say human remains found near Margaret River are believed to be those of missing man Jordan Marshall.
The 40-year-old father of three had been reported missing on December 8 and the last reported sighting was near Mammoth Cave soon after.
A search party that included more than 80 of Mr Marshall's friends and family found the body during a coordinated grid search of the area on Sunday.
Mr Marshall's father, Ross, had told the ABC ahead of the search that he was "hoping not to find anything, but prepared for whatever we do".
The family had also been advocating for better understanding of mental health issues.
Younger brother Daniel said his sibling had been diagnosed with a mental health condition last year and had been "getting active treatment but was becoming increasingly unwell".
Mr Marshall's last sighting occurred just prior to an emergency-level bushfire that is thought to have started near Mammoth Cave and been deliberately lit.
Police maintained the father of three was not linked to the fire, the cause of which is still under investigation.
