Inorganic antiperovskite nitrides have recently emerged as promising materials for photovoltaic applications, yet their nonradiative recombination dynamics remain largely unexplored. Here, we examine the influence of X-site cation substitution on the nonradiative electron-hole recombination in ${\mathrm{X}}_3\mathrm{NSb}$ $(\mathrm{X}=\mathrm{Ca}, \mathrm{Sr}, \text{and} \mathrm{Ba})$. Ca- and Sr-based compounds adopt a cubic phase, whereas Ba stabilizes in a hexagonal structure, introducing pronounced symmetry-driven effects. To separate symmetry effects from cation chemistry, we also examine the hexagonal polymorph of ${\mathrm{Sr}}_3\mathrm{NSb}$ $\left({\mathrm{Sr}}_3{\mathrm{NSb}}_{\mathrm{hexa}}\right)$. Substituting Ca with Sr narrows the band gap, suppresses octahedral and band-edge fluctuations, reduces nonadiabatic (NA) coupling by $\sim 54\%$, and extends carrier lifetimes by a factor of 2.5. In ${\mathrm{Sr}}_3{\mathrm{NSb}}_{\mathrm{hexa}}$, the combination of larger band gap and enhanced band gap fluctuations—leading to faster dephasing—further slows down recombination by $41\%$. In contrast, in ${\mathrm{Ba}}_3{\mathrm{NSb}}_{\mathrm{hexa}}$, enhanced NA coupling accelerates recombination relative to ${\mathrm{Sr}}_3{\mathrm{NSb}}_{\mathrm{hexa}}$. Overall, recombination lifetimes are dictated by the interplay between band gap, NA coupling strength, and decoherence time, with ${\mathrm{Sr}}_3{\mathrm{NSb}}_{\mathrm{hexa}}$ exhibiting the longest lifetime. These findings highlight the coupled influence of cation chemistry and crystal symmetry in tailoring carrier dynamics for high-performance antiperovskite-based optoelectronics materials.

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• Carrier generation & recombination
• Electronic structure
• Excitons
• Perovskites
• Many-body techniques
• Time-dependent DFT