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.