The plastic behavior of MgSiO3 perovskite is investigated under pressure conditions similar to those encountered in the Earth’s lower mantle. The core structures of dislocations with edge and screw characters are determined by means of atomic-scale simulations for the [1 0 0](0 1 0) and [0 1 0](1 0 0) slip systems. The corresponding Peierls stresses increase monotonously with increasing pressure. The edge [0 1 0](1 0 0) dislocation is found to dissociate by climb and to become sessile at high pressure ( GPa). These findings are compared with a continuum Peierls–Nabarro model and with published results in other perovskite materials.