LiBH and Mg(BH) with high theoretical hydrogen mass capacity receive significant attentions for hydrogen storage. Also, these compounds can be potentially applied as solid-state electrolytes with their high ionic conductivity. However, their applications are hindered by the poor kinetics and reversibility for hydrogen storage and low ionic conductivity at room temperature, respectively. To address these challenges, effective strategies towards engineering the hydrogen storage properties and the emerging solid-state electrolytes with improved performances have been summarized. The focuses are on the state-of-the-art developments of Li/Mg-based borohydrides with a parallel comparison of similar methods applied in both hydrogen storage and solid-state electrolytes, particularly on the phase, structure, and thermal properties changes of Li/Mg-based borohydrides induced by milling, ion substitution, coordination, adding additives/catalysts, and hydrides. The similarities and differences between the strategies towards two kinds of applications are also discussed and prospected. The review will shed light on the future development of Li/Mg-based borohydrides for hydrogen storage and solid-state electrolytes.