Abstract: Mn²⁺ doping has been adopted as an efficient approach to regulating the luminescence properties of halide perovskite nanocrystals (NCs). However, it is still difficult to understand the interplay of Mn²⁺ luminescence and the matrix self-trapped exciton (STE) emission therein. In this study, Mn²⁺-doped CsCdCl₃ NCs are prepared by hot injection, in which CsCdCl₃ is selected because of its unique crystal structure suitable for STE emission. The blue emission at 441 nm of undoped CsCdCl₃ NCs originates from the defect states in the NCs. Mn²⁺ doping promotes lattice distortion of CsCdCl₃ and generates bright orange-red light emission at 656 nm. The energy transfer from the STEs of CsCdCl₃ to the excited levels of the Mn²⁺ ion is confirmed to be a significant factor in achieving efficient luminescence in CsCdCl₃:Mn²⁺ NCs. This work highlights the crucial role of energy transfer from STEs to Mn²⁺ dopants in Mn²⁺-doped halide NCs and lays the groundwork for modifying the luminescence of other metal halide perovskite NCs.