Clermontia hanaulaensis H.Oppenheimer, Lorence & W.L.Wagner, sp. nov., a newly discovered, narrowly distributed endemic species, is herein described based on its morphological characteristics and illustrated with field photos and a line drawing. It is currently known only from the slopes of Hana‘ula, in Pōhākea Gulch, Mauna Kahālāwai, west Maui, Hawaiian Islands. It differs from all other species of Clermontia Gaudich. by the combination of its (2)3–4(–5) flowered inflorescence, violet colored perianth often suffused with creamy white streaks or sometimes creamy white with violet-purple irregular veins, (30)35–45(–50) mm long, perianth tube 15–25(–27) mm long, 9–10 mm wide, the lobes 20–26 mm long, (2–)3–3.5 mm wide, with petaloid calyx lobes 1/2–4/5 as long as the petals. A key to the Clermontia species and subspecies occurring on Maui is provided. Its habitat is described. Its conservation status is proposed as critically endangered (CR), and conservation efforts are discussed.