Herein we describe a cation radical-accelerated-nucleophilic aromatic substitution (CRA-SAr) of alkoxy arenes utilizing a highly oxidizing acridinium photoredox catalyst and acetone cyanohydrin, an inexpensive and commercially available cyanide source. This cyanation is selective for carbon-oxygen (C-O) bond functionalization and is applicable to a range of methoxyarenes and dimethoxyarenes. Furthermore, computational studies provide a model for predicting regioselectivity and chemoselectivity in competitive C-H and C-O cyanation of methoxyarene cation radicals.