Lead-free 0.95Bi0.5Na0.5TiO3–0.05BaTiO3 (BNT–5BT) ceramics were Cu/Zr co-doped to improve the electromechanical properties relevant to low-power energy harvesting. Based on the optimized single-dopant contents (1 mol% CuO and 2 mol% Zr), the co-doped composition 0.95(Bi0.5Na0.5)(Ti0.98Zr0.02)O3–0.05Ba(Ti0.98Zr0.02)O3–0.01CuO (BNT–5BT–2Zr–1Cu) was synthesized by solid-state reaction with mechanochemical activation. X-ray diffraction and Raman spectroscopy confirmed the formation of a single perovskite phase and an increased tetragonal contribution compared to the single-doped counterparts, consistent with morphotropic phase boundary (MPB) stabilization. Co-doping increased the ferroelectric–relaxor crossover temperature (TF–R = 195°C) while reducing the room-temperature permittivity, thereby enhancing the piezoelectric voltage response. The co-doped ceramic exhibited ρ = 5.74 g·cm-3, d33 = 130 pC·N-1, and g33 = 10.71×10− 3 V·m·N-1, outperforming the undoped and single-doped reference compositions. These results indicate that Cu/Zr co-doping, combining Cu-assisted densification and defect equilibration with Zr-induced structural tuning, is an effective strategy to enhance the voltage response of lead-free BNT–BT ceramics for low-power energy-harvesting applications.