Scaevola kilaueae is a shrub reaching 0.5–1 meters, though some individuals may grow taller. The leaves are simple, alternate, and oblanceolate, measuring 3–6.8 cm long and 1–1.5 cm wide. The apex is acute, while the base tapers into a petiole 0.7–1 cm long. The surfaces are usually glabrous, and the margins are dentate along the distal half. The leaves are petiolate, and stipules are absent. The flowers occur in cymes of (1–)3–7 flowers, with inflorescence lengths ranging from 30–100 mm. The peduncles measure 15–40 mm long, with the terminal flower sessile and the lateral flowers arranged on pedicels approximately 5 mm long, each subtended by paired bracteoles. The flowers are bisexual and strongly irregular. The calyx is minute and 5-parted. The corolla is funnelform-unilabiate and 5-parted, with the tube adaxially split. The corolla is purplish brown, measuring 20–25 mm long, while the lobes are cream-colored with purple lines, 8–10 mm long, with winged margins. The throat is pale yellowish brown. The five stamens are distinct and slightly shorter than the corolla tube. The anthers are introrse, dithecal, and dehisce via longitudinal slits, with pollen being shed from the coherent anthers and collected by the indusium on the outgrowing style. The ovary is inferior and ovoid, with two cells and axile placentation. The style, measuring 23–30 mm long, is exserted and protrudes through the adaxially split corolla tube, curving abruptly downward near the stigma, which is 1–2-lobed. The fruit is a drupaceous, 2-celled, dark purplish-black ovoid structure, approximately 10 mm long. The surface is either glabrous or sparsely pubescent. Seeds vary from one to numerous and contain oily endosperm. It is found in localized populations on old lava flows and ash substrates, often within open Metrosideros forests and shrublands between 1,000-1,460 meters.