Na_0.5Bi_0.5TiO₃ (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO₃ (BT) was introduced to the 0.94Na_0.5Bi_0.5TiO₃-0.06Bi(Mg_2/3Nb_1/3)O₃ system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na_0.5Bi_0.51TiO₃-xBaTiO₃]-0.06Bi(Mg_2/3Nb_1/3)O₃ (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum P_max (38.29 μC/cm²) and E_b (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of W_rec ~ 1.02 J/cm³ and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications.