Ternary piezoelectric ceramics Pb(In1∕2Nb1∕2)O₃–Pb(Mg1∕3Nb2∕3)O₃–PbTiO₃ (PIN–PMN–PT) exhibit excellent temperature stability and hold great potential for high-frequency and high-power applications. However, its piezoelectric performance is much lower than that of the famous binary Pb(Mg1∕3Nb2∕3)O₃–PbTiO₃ (PMN–PT) system. In this work, high-performance 15PIN–50PMN–35PT piezoceramics with piezoelectric coefficient d33 of 700 pC/N, electromechanical coupling coefficient kp of 66% and high Curie temperature TC of 199°C were fabricated. Effect of Samarium (Sm) doping content on the ferroelectric, dielectric, electromechanical and piezoelectric properties and structures of 15PIN–50PMN–35PT piezoelectric ceramics were investigated, and results reveal that increasing the amount of Sm doping leads to a significant decrease of d33, kp, TC and other properties. This phenomenon is different from the previously reported results in Sm-doped binary PMN–PT ceramics. The room temperature and variable temperature phase structure and room temperature microstructure were studied to explain this phenomenon.