Grevillea diffusa is a species of flowering plant in the family Proteaceae and is endemic to the Sydney region of New South Wales.

[3][4][5][6] Grevillea diffusa was first formally described in 1827 by Kurt Polycarp Joachim Sprengel in Systema Vegetabilium from an unpublished description by Sieber.

[9] In 1986, Donald McGillivray described subspecies of G. diffusa in his book New Names in Grevillea (Proteaceae), and in 2000 Robert Owen Makinson described subspecies in Flora of Australia, and the following three names are accepted by the Australian Plant Census: This grevillea grows in forest or woodland, occasionally in swampy heath and is restricted to Hawkesbury sandstone in the Sydney basin.

Although its distribution is restricted, the population of this species is presumed to be stable and there are currently no major threats impacting it.

Increased fire regimes may pose a minor threat in some areas of its distribution.