[Pb(Mg1/3Nb2/3)O3]0.69(PbTiO3)0.31 single crystal of composition close to the morphotropic phase boundary has been studied by dielectric spectroscopy in the frequency range of 1–1000 kHz under hydrostatic pressure (p) up to 0.6 GPa. At ambient pressure two successive phase transitions have been observed: the monoclinic-tetragonal transition at T1 = 346 K and the transition from the ferroelectric tetragonal to the cubic relaxor phase at TC = 415.7 K. At elevated pressures the temperature range of the ferroelectric tetragonal phase diminished, while the relaxor phase evolved. The p-T phase diagram shows that pressure decreases linearly T1 and TC, as well as the temperature Tm of the relaxor peak, but with different slopes: dT1/ dp = −(2.6 ± 1.6) K/GPa, dTC/ dp = −(55.5 ± 0.2) K/GPa and dTm(10 kHz)/ dp = −(48.7 ± 1.0) K/GPa.