Abstract: This study employs density functional theory (DFT) calculations to systematically investigate the B‒H bond dissociation enthalpies (BDEs) of Lewis base‒borane complexes. A rigorous benchmark analysis identified the ωB97X-D/cc-pVTZ method as a reliable method for accurate prediction of B–H BDEs. An examination of more than 200 structurally diverse complexes across five major classes revealed that the type of Lewis base significantly influences the BDEs, with the order of amine–borane > phosphine–borane > N-heterocyclic carbene–borane > pyridine–borane. Solvent-stabilized boranes exhibit the broadest range of BDE values due to the diverse coordination modes of solvent molecules with borane. Further analysis revealed that the BDE values are synergistically affected by skeletal and substituent effects. Notably, a strong linear correlation (R² up to 0.97) between the spin density of boryl radicals and BDEs, except for amine–boranes, provides a robust predictive model. This research enhances the fundamental understanding of B‒H bond dissociation properties in Lewis base–boranes and provides valuable insights for the development of new boron-based methodologies in organic synthesis.