Dearomative functionalization of heteroarenes offers an attractive and sustainable approach for the rapid construction of complex 3D heterocyclic scaffolds from planar structures. Despite progress in this field, dearomative amination of heteroarenes via a radical anion intermediate remains a challenge. Here, we report a photoredox-catalyzed dearomative hydroamination of heteroarenes with hydrazodiformates under mild and transition-metal-free reaction conditions. Various benzofurans and benzothiophenes can efficiently participate in this transformation. A series of mechanistic experiments revealed that heteroaryl radical anions are the crucial intermediates, generated through photo-induced electron transfer between the excited phenolate photocatalyst and heteroarenes.