The genus Stenobelus Zimmerman,1999 of the weevil tribe Belini Schoenherr, 1826 currently contains two species, Stenobelus testaceus (G. R. Waterhouse, 1839) and S. tibialis (Blackburn, 1893). Both species were described from southwest Western Australia (WA), and S. testaceus is the first weevil species described from the specimens collected by Charles Darwin in Australia in 1836 (Oberprieler et al. 2010). Now, a third species, Stenobelus minutus Glatz, sp. nov., is described from a single specimen collected 180 years later, in 2016, at East Mount Barren in the Fitzgerald River National Park at the south coast of WA. This is the first new Stenobelus to be described in 131 years. It is compared with the two previously described species, from which it most obviously differs by size, and the form of the elytra and dorsal vittae. A key is provided to distinguish the three known Stenobelus species.