Achieving high piezoelectric performance in BiFeO3–BaTiO3-based ceramics while enhancing the stability of the piezoelectric coefficient (d33) during depolarization presents a significant challenge. The poor thermal stability stems from intrinsic defects and disruption of the long-range ferroelectric order induced by doping with foreign elements. This study employs a two-step synthesis strategy, combining long-range-ordered ferroelectrics with relaxor ferroelectrics. By modifying the domain-structure characteristics, the energy barrier for switching polar structures is increased, thereby enhancing the thermal stability. This process yields a high d33 value (93 pC N−1) and high depolarization temperature (Td ≈ 650 °C) while effectively mitigating the continuous decline in d33 observed in relaxor ferroelectrics from room temperature to Td. After depolarization at 650 °C for 3 hours, the variation in d33 (Δd33/d33) was only 17.2%. The resistivity (ρ) remained high at 1.3 × 106 Ω cm at 300 °C. Ultrasonic experiments based on this piezoelectric material confirmed that at 300 °C, the symmetric (S0) and antisymmetric (A0) zero-order modes maintained high signal-to-noise ratios of 21.6 dB and 20.3 dB, respectively. These results highlight the strong potential of the ceramic for high-temperature ultrasonic structural health monitoring (SHM) systems.