<p>Bismuth titanate-ferrite (Bi₅Ti₃FeO₁₅) is a promising candidate for high-temperature piezoelectric applications owing to its high Curie temperature <i>T</i>_C of 761°C. However, its practical utility is limited by its low piezoelectric response and insufficient electrical resistivity at elevated temperatures. In this study, lanthanum-substituted Bi₅Ti₃FeO₁₅ ceramics were synthesized via the conventional solid-state sintering method to address these limitations. The structural, piezoelectric, and electrical properties were investigated in detail. The results demonstrate that lanthanum substitution significantly enhances both piezoelectric and electrical characteristics. A notable piezoelectric coefficient <i>d</i>₃₃ of 24.3 pC/N is achieved, which is over three times that of pristine Bi₅Ti₃FeO₁₅ (7.1 pC/N), along with a high <i>T</i>_C of 753°C and excellent thermal stability of electromechanical coupling factors up to 400°C. Furthermore, alternating-current and direct-current conduction analyses indicate that the improved resistivity stems from a reduced concentration and mobility of oxygen vacancies. The optimized composition exhibits maximum dc resistivity <i>ρ</i>_dc of 3.62 × 10⁵&#xa0;Ω cm at 500°C, an order of magnitude higher than that of the unsubstituted counterpart. These enhancements in piezoelectric performance and high-temperature electrical resistivity position lanthanum-substituted Bi₅Ti₃FeO₁₅ ceramics as strong candidates for high-temperature piezoelectric sensor applications.</p>