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The electrical and optical properties of (001)‐ and (110)‐oriented 0.73 Pb(Mg1/3Nb2/3)O3‐0.27PbTiO3 single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field‐induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d33* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN‐0.27PT single crystals with (001)‐ and (110)‐orientations under a low electric field show ultrahigh d33* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field‐induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy. The 0.73PMN‐0.27PT single crystals present a series of ferroelectric phase transition processes, which is confirmed by dielectric performance measurement, polarized light microscopy and Raman spectra contour plot. The electric field induced monoclinic and orthorhombic phase contribute to the ultra‐high d33- in the (001)‐ and (110)‐orientations crystals. [ABSTRACT FROM AUTHOR]