Heteroarenes are structural motifs found in many bioactive compounds and functional materials. Dehydrogenative cross‐coupling of heteroarenes with aliphatic C−H bonds provides straightforward access to functionalized heteroarenes from readily available materials. Established methods employ stoichiometric chemical oxidants under conditions of heating or light irradiation. By merging electrochemistry and photochemistry, we have achieved efficient photoelectrochemical dehydrogenative cross‐coupling of heteroarenes and C(sp3)−H donors through H2 evolution, without the addition of metal catalysts or chemical oxidants. Mechanistically, the C(sp3)−H donor is converted to a nucleophilic carbon radical through H‐atom transfer with chlorine atom, which is produced by light irradiation of anodically generated Cl2 from Cl−. The carbon radical then undergoes radical substitution to the heteroarene to afford alkylated heteroarene products. An efficient photoelectrochemical dehydrogenative cross‐coupling of heteroarenes with C(sp3)−H species is described. Chlorine atoms, which are produced by light irradiation of anodically generated Cl2 from Cl−, a hydrogen atom from C(sp3)−H bonds to afford carbon radicals. The latter undergo Minisci alkylation to afford the final functionalized heteroarene products.