Hakea megadenia is an upright bushy spreading shrub or small tree high. The branchlets are covered densely in flattened hairs. The dull green leaves are needle-shaped or flattened long and wide ending in a sharp point. The inflorescence on female plants has 1–8 flowers and the male 3–14 flowers. The overlapping bracts long, the inflorescencestalk long hairy and rust coloured. The pedicel long with white flattened dense silky hairs extending to the whitish long perianth. The fruit are S-shaped, long and wide. The white to cream flowers appear in leaf axils from February to July.
This species is found on the east coast of Tasmania and the Furneaux group of islands. Growing at lower altitudes in coastal areas, river bushland or drier forest. On the islands it grows at higher altitudes with longer leaves and perianth and larger fruit.