In this study, we investigated the effect of zirconium content on lead-free barium zirconate titanate (BZT) (Ba(Zr_xTi_1−x)O₃, with x = 0.00, 0.01, 0.03, 0.05, and 0.08), which was prepared by the sol–gel method. A single-phase perovskite BZT was obtained under calcination and sintering conditions at 1100 °C and 1300 °C. Ferroelectric measurements revealed that the Curie temperature of BaTiO₃ was 399 K, and the transition temperature decreased with increasing zirconium content. At the Curie temperature, Ba(Zr_0.03Ti_0.97)O₃ with a dielectric constant of 19,600 showed the best performance in converting supplied mechanical vibration into electrical power. The experiments focused on piezoelectric activity at a low vibrating frequency, and the output power that dissipated from the BZT system at 15 Hz was 2.47 nW (30 MΩ). The prepared lead-free sol–gel BZT is promising for energy-harvesting applications considering that the normal frequencies of ambient vibration sources are less than 100 Hz.