A developmental process, independent of morphogenetic (shape) change, that is required for the glossopharyngeal nerve to attain its fully functional state. Various sensory and motor branches of the glossopharyngeal nerve supply nerve connections to the pharynx and back of the tongue. The branchial motor component contains motor fibers that innervate muscles that elevate the pharynx and larynx, and the tympanic branch supplies parasympathetic fibers to the otic ganglion. [ http://purl.obolibrary.org/obo/go/references/0000021 GOC:dgh https://www.worldcat.org/search?q=bn%3A0838580343 GOC:cls GOC:jid GOC:dph ]