Abstract The effect of minor additions of excess MgO and PbO on the sintering characteristics, microstructure development and dielectric properties of perovskite-based Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 solid solutions was investigated. Both MgO and PbO are compatible with the Pb(Mg 1/3Nb 2/3)O 3-based solid solutions and thus, these phases co-exist with one another during sintering at elevated temperatures. On sintering a solid solution composition Pb[(Mg 1/3Nb 2/3) 0.9Ti 0.1]O 3 with minor additions of MgO, the excess MgO remained as a discrete phase in the ceramics at temperatures up to 1230 °C and inhibited grain growth. Above this temperature, MgO combined with the solid solution to form a liquid phase, which caused an enhancement of the densification process. On sintering the solid solution with excess PbO, a low-temperature melting PbO-rich liquid phase was formed, which promoted the densification process with inhomogeneous grain growth. Simultaneous additions of 1.0 wt.% MgO and 2.0 wt.% PbO to the Pb[(Mg 1/3Nb 2/3) 0.9Ti 0.1]O 3 solid solution and sintering the resulting material at 1000 °C for 3 h led to the formation of a dense and homogeneous microstructure consisting of evenly distributed grains with an average grain size of 10 μm. The peak dielectric constant of this composition (at ≈38 °C), measured at a frequency of 1 kHz, was 18,000 with a dissipation factor of <2%.