Lead-based perovskites have been prominently featured across diverse fields. Nevertheless, the intrinsic toxicity associated with lead compounds presents substantial environmental and health concerns. Thus, it has become imperative to seek alternatives devoid of lead. Our research presents a pioneering solution to this predicament by zeroing in on cesium-manganese-bromide-based perovskite crystals. Our research involves doping the pseudohalide anion acetate (Ac⁻) into halide positions within CsMnBr₃·2H₂O crystals, resulting in a remarkable improvement in their luminescence characteristics. The optimized CsMnBr₃·2H₂O:Ac⁻ crystals displayed a photoluminescence quantum yield (PLQY) surpassing 70%, marking a substantial advancement compared to the modest PLQY observed in pristine CsMnBr₃·2H₂O bulk crystals. Theoretical analysis was employed to ascertain the precise lattice position occupied by Ac⁻. High-performance ion chromatography confirmed the presence of Ac⁻ and determined the pseudohalide concentration. Studies on carrier dynamics to investigate the impact of Ac⁻ on CsMnBr₃·2H₂O revealed that the significant enhancement in emission following Ac⁻ doping is linked to the mitigation of nonradiative carrier trapping processes. The differences in Mn–Mn dipole–dipole and spin-exchange interactions were verified through electron paramagnetic resonance, magnetic measurements and femtosecond transient photoluminescent spectroscopy. The experimental data prove that the doping of Ac⁻ leads to a decrease in spin-exchange interaction, which consequently decelerates the separation of holes and electrons, subsequently facilitating the recombination process. Our study provide valuable insights into the mechanism by which pseudohalide affects the perovskite sample, with Ac⁻ suppressing non-radiative recombination processes and also influencing the exciton dissociation, leading to enhanced efficiency in radiative recombination processes. The findings furnish a promising method of conditioning the properties of perovskite crystals, which offers a new way for materials design towards diverse emerging applications.