The elastic, piezoelectric, and dielectric properties of [001]c and [011]c poled 0.33Pb(In1/2Nb1/2)O3-0.38Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals have been fully characterized at room temperature, and the temperature and frequency dependence of the dielectric susceptibility ε33 were also measured. The depoling temperature of this crystal is more than 20 °C higher than that of the corresponding binary 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 system. From the measured P-E hysteresis loops, the coercive fields along [001]c and [011]c directions have been determined to be 6.0 kV/cm and 6.6 kV/cm, respectively, which indicate that these domain engineered ternary relaxor-based ferroelectric single crystals are excellent candidates for high-power applications.