This goshawk is recorded on New Britain in Papua New Guinea. A 2025 paper describes how to distinguish it from another goshawk on the island.
In a comparison with the New Britain Goshawk, the adult Slaty-mantled Goshawk is described as darker above, with a buff wash and faint grey barring below.
The species account lists open forest, forest edges and partly cleared areas as habitat. Its records extend from sea level to 700 m.
An extinction-risk assessment has not been added yet.