Grevillea oncogyne is a shrub of the genus Grevillea native to an area in the eastern Wheatbelt and south-western Goldfields-Esperance regions of Western Australia. The many branched shrub typically grows to a height of 1 to 3 metres (3 to 10 ft) and has non-glaucous branchlets. It has simple flat linear leaves with a blade that is 35 to 115 millimetres (1.4 to 4.5 in) in length and 1 to 2 mm (0.04 to 0.08 in) wide. It blooms from October to December and produces an axillary raceme irregular inflorescence with red or pink flowers. Later it forms ribbed or ridges ellipsoidal fruit that is 7 to 15 mm (0.3 to 0.6 in) long.