The development of piezoelectric ceramics characterized by both large piezoelectric response and high temperature stability is imperative for the advancement of practical electromechanical devices. However, existing high-performance piezoelectric ceramics often encounter compromised temperature stability due to ferroelectric phase transitions occurring within low-temperature regions. In this work, we focused on Sm-doped Pb(Ni_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PNN-PZT:Sm) ceramics with tetragonal (T)-phase structure to achieve the desired combination of large piezoelectricity and high temperature stability. The results indicate that 2 mol% Sm-doped samples exhibit a large piezoelectric constant d₃₃ of 575 pC/N, an effective piezoelectric strain coefficient d₃₃^* of 890 pm/V, and a high T_m of 279 °C. Remarkably, the d₃₃ experiences only a 2.6% variation over the temperature range of 30 °C to 250 °C, while the d₃₃^* changes by 8% within the temperature range of 30 °C to 180 °C. Microstructural and domain structure analyses suggest that Sm-doing effectively reduces the grain size, leading to decreased domain size, thereby achieving excellent electromechanical properties. The superior temperature stability is attributed to the suppressive effect of Sm-doping on the R-T ferroelectric phase transition. These studies suggest that Sm-doping represents an effective strategy for achieving the collaborative optimization of piezoelectricity and temperature stability through grain and domain engineering techniques for perovskite ferroelectric materials.