Visible-light-induced halide-exchange between halide perovskite and organohalide solvents has been studied in which photo-induced electron-transfer from CsPbBr3 nanocrystals (NCs) to dihalomethane solvent molecules produces halide anions via reductive dissociation, followed by a spontaneous anion-exchange. Photo-generated holes in this process are less focused. Here, for CsPbBr3 in dibromomethane (DBM), we discover that Br radical (Br•) is a key intermediate resulting from the hole-oxidation. We successfully trapped Br• with reported methods and found that Br• is in continuous generation in DBM under visible light irradiation, hence imperative for catalytic reaction design. Continuous Br• within this halide-exchange process is active for photocatalytic [3+2] cycloaddition for vinylcyclopentane synthesis, a privileged scaffold in medicinal chemistry, with good yield and rationalized diastereoselectivity. The NCs photocatalyst is highly recyclable due to Br-based self-healing, leading to a particularly economic and neat heterogeneous reaction where the solvent DBM also behaves as a co-catalyst for perovskite photocatalysis. Halide perovskites, notable for efficient solar energy conversion, herein are demonstrated as an exceptional photocatalyst for Br radical-mediated [3+2] cycloaddition. We envisage such perovskite-induced Br radical strategy may serve as a powerful chemical tool to develop valuable halogen radical-involved reactions.