Bennett's chinchilla rat is the largest species in the genus, with an average head-and-body length of 206 mm (8 in) and a tail about 80% of this.

As with other members of the genus, the fur is long, dense and soft, and the ears prominent and rounded.

The dorsal surfaces of both fore and hind feet are clad in whitish fur while the undersurfaces are pigmented but un-furred.

[4] A. bennettii has an extensive range in Chile on the western slopes of the Andes where it is found at altitudes up to about 2,000 m (6,600 ft).

The habitat is being degraded by conversion to agricultural land and by mining, but this chinchilla rat is present in several protected areas and any downward trend in populations is slow, so the International Union for Conservation of Nature has assessed its conservation status as being of "least concern".