[3] The Porongurup Range forms part of the Southwest Biodiversity Hotspot,[4] which is one of 34 regions in the world noted for a rich diversity of flora and fauna species.

The range is the remnant of a sizeable reservoir of molten granite that bubbled up when the Antarctic continent struck Australia in the Stenian Period of the Mesoproterozoic Era, around 1200 million (1.2 billion) years ago.

Examples of plant groups present include: heaths (Epacridaceae), especially beard-heaths (Leucopogon); peas (Fabaceae), notably flame-peas (Chorizema), bitter-peas (Daviesia and Bossiaea) and poison-peas (Gastrolobium); native myrtles (Myrtaceae); pimeleas (Thymelaeaceae), notably rice flowers (Pimelea); sundews and pitcher plants (Nepenthales); bloodroots, conostyles, kangaroo paws and their allies (Haemodorales); and banksias and grevilleas (Proteales).

[3] A remnant island of karri forest prevails here, hundreds of kilometres east of the cool southwest cape where they are more commonly found.

[12] On lateritic soils downslope, the predominant type of vegetation is a mixed forest of jarrah and marri, whilst on the highly exposed and frequently waterlogged summits, an open mossy herbland prevails.

[12] Seventy-one bird species including the red-eared firetail (Emblema oculata) and Baudin's black cockatoo (Calyptorhynchus baudinii) are also found in the park.

[12] At least 17 reptile species are known to inhabit the park including King's skink (Egernia kingii), the southern heath monitor (Varanus rosenbergi) and the marbled gecko (Phyllodactylus marmoratus).

Invertebrates present in the National Park include Gondwanan relictual species such as the Porongurup trapdoor spider (Neohomogona bolganupensis), land snails (Bothriembryon spp.)

In 1978, Cyclone Alby felled many trees within the National Park (it was an unusual depression that produced very little rainfall after moving south of the Tropic of Capricorn).

By early April, Kingia australis plants were re-shooting and flowering abundantly in heavily burnt areas but the legacy of the fire will be felt for some time to come.