An environmentally friendly electrochemical approach for iodoamination of various indole derivatives with a series of unactivated amines, amino acid derivatives, and benzotriazoles (more than 80 examples) has been developed. This strategy was further applied in late-stage functionalization of natural products and pharmaceuticals and gram-scale synthesis and radiosynthesis of 131I-labeled compounds. Fundamental insights into the mechanism of the reaction based on control experiments, density functional theory calculation, and cyclic voltammetry are provided.