A newly discovered ammonoid, Mimagoniatites nearcticus n. sp., is described from upper Zlichovian–lower Dalejan (Lower Devonian) strata in the Canadian Arctic Archipelago. This species is distinguished primarily by its extremely narrow profile and high degree of whorl involution. It is the most gracile species so far known in the genus, and displays possible kinship to Parentites praecursor Bogoslovsky. This record constitutes the first definite occurrence of a Lower Devonian ammonoid from the Canadian Arctic Archipelago.