Senior constable Kristian White was called to the nursing home in May 2023 as Clare Nowland -- who displayed symptoms of dementia -- slowly roamed the halls with a steak knife.
After repeatedly asking for an agitated Nowland to drop the knife, White said "bugger it" and shot his stun gun, the New South Wales Supreme Court heard.
The great grandmother fell backwards, hit her head, and died in hospital a week later from a brain bleed.
Nowland reportedly weighed less than 50 kilograms (110 pounds) at the time, and police would later describe her as "frail".
A jury on Wednesday found 34-year-old White guilty of manslaughter after three days of deliberations, a court official said.
White pleaded not guilty, arguing that he had taken legitimate steps to resolve a possible threat.
Police rejected accusations they had tried to cover up the scandal by scrubbing terms such as "taser" from an initial statement.
