Highly accelerated lifetime tests (HALTs), thermally stimulated depolarization current (TSDC), and impedance spectroscopy (IS) measurements were performed on 0.7 Pb(Mg1/3Nb2/3)O3−0.3 PbTiO3 (PMN-PT) single crystal to investigate time dependent dc resistance degradation under a dc bias. A low activation energy of 0.61±0.04 eV which controls the degradation process in PMN-PT single crystal is determined from the characteristic degradation time tC in HALT. Meanwhile, in a complementary TSDC investigation, a broad depolarization peak with an activation energy of 0.6±0.03 eV is observed in virgin PMN-PT single crystal having the characteristics of ionic space charge. Finally, impedance spectra of degraded PMN-PT single crystal exhibited three relaxations in contrast to two relaxations in virgin PMN-PT single crystal. In terms of equivalent circuit, an element combination R-ZCPE corresponding to ionic conduction is common to both virgin and degraded single crystals, and an activation energy about 0.64 eV, attributed to the ionic transport, is also obtained. This value is low compared to similar studies on alkaline-earth titanate perovskites, such as Fe-doped SrTiO3, however, here we suggest the activation energy about 0.6 eV from three independent measurements is attributed to the migration of oxygen vacancies in this particular lead-based single crystal, and besides this apparent ionic conduction, band electronic conduction is also discussed in both virgin and degraded single crystals in this paper.