The case was confirmed in a devil that was found dead on the side of the road in the state's remote northwest.
It was the first case detected on Harcus River Road, about 20km from the closest previous confirmed cases, Tasmania's Department of Natural Resources and Environment said.
Save the Tasmanian Devil Program manager Billie Lazenby said the result was "really disappointing" but not surprising.
"That far northwestern corner is one of the last known disease-free areas in the state," she said.
"This (case) means that we know that the disease is likely to have spread further into there."
Devil Facial Tumour Disease (DFTD), an aggressive, non-viral, transmittable parasitic cancer, was first detected in northeast Tasmania in the mid-1990s.
It has since spread, wiping out 80 per cent of the devil populations it hits.
There is no diagnostic test for the disease, which means it is unable to be detected until devils develop physical symptoms.
The recent case was confirmed after a member of the public spotted the devil with suspected lesions and reported it to the department.
"We will need more information to understand if this is an isolated diseased devil or whether the disease affects a larger proportion of the devil population in the area," Dr Lazenby said.
Numbers of the Tasmanian devil, which is listed as endangered, are expected to further decrease as a result of the disease, stabilising between 7000 and 10,000 in the next decade.
Dr Lazenby said while the origin of DFTD remained a mystery there were very early signs at a genetic level that the species was developing resistance.
"That's accepted as a possibility (but) we haven't yet seen that playing out on the ground," she said.
"What we have observed widespread across Tasmania is that devil populations have compensated for Devil Facial Tumour Disease.
"They've done that by breeding younger. One-year-old females are breeding now, where in non-diseased populations that was quite rare."
Dr Lazenby said disease-free "insurance populations" existed in captivity across Australia, as well as one on Maria Island off Tasmania's east coast.
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