Piezoelectric 0.365BiScO3-0.635PbTiO3 (BSPT) ceramics are promising for high temperature actuator applications due to their high Curie temperature and high piezoelectric coefficient. However, relatively low mechanical quality factor (Qm ≈ 25) and high dielectric loss (tan δ ≈ 0.04) would lead to self-heating and property degradation if BSPT ceramics are used in piezoelectric actuators that work at resonant frequency. In this work, Mn-doped BSPT ceramics were prepared by conventional solid state reaction to modify the electrical properties. Excellent hard piezoelectric properties of d33 ≈ 200 pC/N, Qm ≈ 210, and tan δ ≈ 0.015 were measured in the BSPT ceramics doped with 1.2 wt% of Mn. Further, Mn-doped BSPT ceramics showed a depoling temperature of 360 °C, about 100 °C higher than that of commercialized hard PZT ceramics. These results indicate that piezoelectric actuators fabricated with Mn-doped BSPT ceramics would exhibit enhanced thermal stability and higher energy efficiency in a wide temperature range.