The top of the island is capped with Drooping Sheoak (Allocasuarina verticillata) and Dryland Tea-tree (Melaleuca lanceolata) woodlands while the lower slopes have either a Coastal Tussock (Poa poiformis var.

[1] The island features haul-out areas for Australian sea lion and New Zealand fur seal.

[1] The Australian sea lion, previously known as a "hair seal" was observed by visitors to Greenly Island in 1948.

Birds recorded on Greenly Island include the Cape Barren goose, white-faced heron, ruddy turnstone, Australian raven, Nankeen kestrel, white-bellied sea eagle, sooty oystercatcher, welcome swallow, silver gull, Pacific gull, rock parrot, little grassbird, red-capped robin, great cormorant, short-tailed shearwater, crested tern, fairy tern, silvereye and little penguin.

[7] Greenly Island first obtained protected area status as a fauna conservation reserve declared under the Crown Lands Act 1929-1966 on 16 March 1967 .