Molecular aggregation affects the electronic interactions between molecules and has emerged as a powerful tool in material science. Molecular aggregation finds wide applications in the research of new physical effects; however, its value for chemical reaction development has been far less explored. Herein, we report the development of aggregation-enabled alkene insertion into carbon–halogen bonds. The spontaneous cleavage of C–X (X = Cl, Br, or I) bonds generates an intimate ion pair, which can be quickly captured by alkenes in the aggregated state. Additional catalysts or promoters are not necessary under such circumstances, and solvent quenching experiments indicate that the aggregated state is critical for initiating such sequences. The ionic insertion mode and the intimate ion pair mechanism are supported by mechanistic studies, density functional theory calculations, and symmetry-adapted perturbation theory analysis. Results show that the non-aggregated state may quench the transition state and terminate the insertion process.