The Normanby perchlet Plectranthias normanby n. sp. is described from off Normanby Island, Milne Bay Province, Papua New Guinea, Solomon Sea, western Pacific Ocean, based on 2 specimens collected at depths of 175-480 metres. The new species is characterised within the Plectranthias inermis species group by the dorsal in with 12 spines and 13 soft rays; no dorsal-fin rays filamentous; fourth dorsal-fin spine the longest, the spine length 2.25-2.34 in head; anal fin with 3 spines and 7 soft rays; pectoral-fin rays 13, none branched; branched caudal fin emarginate without filamentous rays; branched caudal-fin rays 13; no scales on anterior half of interorbital space; gill rakers 7 + 10-11; posterior margin of preopercle with 11-19 serrae, lower margin with 2 antrorse spines; lateral line incomplete, with 17 tubed scales; scales above lateral line to origin of dorsal fin 3½; scales below lateral line to origin of anal fin 9; circumpeduncular scales 14; cheek with ca. 5 diagonal rows of large scales; sides of body with a large, round black blotch, caudal peduncle with two dark brown spots. A key to the species of the Plectranthias-inermis species-group is presented.