Mild blue light-mediated N-H insertion of indole and its derivatives into aryldiazoesters has been reported in a batch and flow strategy to afford the corresponding N-alkylated product in moderate-to-excellent yield. Detailed high-performance liquid chromatography-based reaction kinetics measurements, control experiments, and kinetic isotope effect reveal that 3-substituted indoles with electron-withdrawing groups such as -CN and -CHO facilitated the product formation, whereas the electron-donating group retarded the process. The neutral indole performed in between them. Furthermore, Hammett plot and density functional theory-based transition-state optimization studies showed substantial correlation of the electronic nature of the substituents at the C3 position of indoles with the rate of the N-H insertion reaction. The strategy was utilized to synthesize a key intermediate for the natural product (-)-psychotrimine.