1610s, from Latin narrator "a relater, narrator, historian," agent noun from narrat-, stem of narrare "to tell, relate" (see narration). In sense of "a commentator in a radio program" it is from 1941.
1748, back-formation from narration or else from Latin narratus, past participle of narrare "to tell, relate, recount" (see narration). "Richardson and Johnson call it Scottish" [OED], a stigma which kept it from general use until 19c. A few mid-17c. instances are traceable to Spanish narrar. Related: Narrated; narrating.