(0.85−x)Pb(Mg1/3Nb2/3)O3–0.10Pb(Fe1/2Nb1/2)O3–0.05PbZrO3–xPbTiO3 [(0.85−x)PMN–0.10PFN–0.05PZ–xPT] polycrystalline ceramics with morphotropic phase boundary (MPB) compositions were prepared using the modified columbite precursor method. The phase transitional behaviors, composition-dependent electrical properties, and temperature-dependent piezoelectric properties were investigated, respectively. XRD and Raman spectrum analysis indicated that MPB compositions were located around the region with the PT content of x = 0.30–0.34, confirmed by their corresponding dielectric, piezoelectric, and electromechanical properties. The composition with x = 0.32 possessed the optimum properties with dielectric permittivity εr, tangent loss tan δ, piezoelectric coefficient d33, electromechanical coupling coefficient kp, remnant polarization Pr, and coercive field Ec of 3432, 0.017, 626 pC/N, 0.56, 29.90 μC/cm2, and 7.23 kV/cm, respectively. The phase diagram mapped indicated that this quaternary system possesses the similar MPB region with that of other binary and ternary systems. The quaternary system PMN–PFN–PZ–PT possessed more competitive d33, kp, and Tr−t than that of Fe-free ternary 0.59Pb(Mg1/3Nb2/3)O3–0.05PbZrO3–0.36PbTiO3 (0.59PMN–0.05PZ–0.36PT) near MPB, exhibiting comparable Pr, Ec, εr, tan δ, and Tc. Temperature-dependent field-induced-strain and the as-calculated high field d33 also confirmed higher temperature stability for Fe-contained PMN–PFN–PZ–PT.