The species has even been reported to sometimes turn up in forest edge and relatively open areas such as gardens, but more extensive research that this is extraordinarily rare if it does even occur.

The back bears faint buff and white edging, which in good light can make these areas appear somewhat scaled.

The tail is of the same colour as the back with a whitish tip with four or five blackish bands (the subterminal one being broad), which are also present on the cream-colored undertail.

The Papuan eagle has rather peculiar proportions, with a prominent head, powerful, large and black bill and cere, large eyes with brown to orange irises, a chesty build, extremely elongated, bare legs of a brownish-grey to dull orange colour, very long tail, and powerful feet with sharp claws.

Despite their distinctive appearance, the honey buzzard is not infrequently mistaken for a Papuan eagle in the dense, dark forests.

[9][10][15] Typically, this species is known to perch inconspicuously in thick canopy and can be fairly difficult to see as it often slips away quietly, seemingly to avoid human detection.

[2][10] Due to its occasional tendency to vocalize at night, large eyes, and almost owl-like facial area, this species has at times been hypothesized to be an occasional nocturnal hunter, but the Papuan eagle has never been proven to hunt by night and is now thought to be a diurnal hunter like other eagles.

[4][17] The Papuan eagle is also known to spend a fair amount of time on the ground and to run with considerable agility and surprising speed, apparently whilst hunting for prey such as megapodes.

[4][8] One food study in Crater Mountain Wildlife Management Area reinforced the primary importance of phalangers, as more than half of 29 prey items were these marsupials.

[7] However, a different study of the same wildlife management area showed a preference for Dorcopsulus forest wallabies, which comprised 6 of 10 prey items.

[16] However, data do indicate the Papuan eagle is an opportunistic predator and can take a wide range of birds including pigeons and doves, hornbills, cockatoos, megapodes and juvenile cassowaries.

[2] Much of the recorded prey of Papuan eagles is fairly large, most species targeted by them weighing in adults 0.5 to 1 kg (1.1 to 2.2 lb) or considerably more, a Matschie's tree-kangaroo weighing 6 kg (13 lb) was recorded as prey of Papuan eagles.

[7][16][20] Singing dogs, established exotic wild animals analogous to Australia's dingos, are known to steal the bird's kills.

[21] An incident of the apparent act of predation by a Papuan eagle on a small child has been considered "thought authentic" by some authors and "very dubious" by others.

[2][4][22] The Papuan eagle was thought to become the only remaining top predator of the island after the extinction of local giant monitor lizards and possibly large carnivorous marsupials.

[23] It is not known how Papuan eagles co-exist with the similarly sized Gurney's eagles, which also frequents rainforest and appears to select somewhat similar prey, but the Gurney's seems more prone to appearing in lower elevation forests (i.e. reportedly very rare above 1,500 m (4,900 ft) and more likely to visit forest openings.

[8] A specimen in breeding condition was recorded in June, actively nest building in April–May and having large nestlings in August.

[8] Large, emergent trees appear to be preferred, with some genera the eagles have been known to nest being Eugenia, Syzygium and Aglaia.

These feathers were known to historically be highly prized possessions, although the Papuan eagle may also be shot or otherwise killed out of competition for bushmeat with local people.

Evidence suggests that the active killing of Papuan eagles is quite ongoing well into the 21st century, and is probably entirely unsustainable given the already low population size.