Ferroelectric low-tolerance-factor perovskites are gathering a lot of attention in the search for novel perovskite solid solutions with a morphotropic phase boundary, which present the highest piezoelectric coefficients known. However, thermodynamic stability is an issue, and powders and ceramics of a number of compositions in very promising systems cannot be synthesized and processed but by high-pressure techniques. This is the case of Pb(Zn1/3Nb2/3)O3−PbTiO3 with piezoelectric coefficients as high as 2500 pC N-1 and of the BiMO3−PbTiO3 (M for metal) systems with a high Curie temperature, which are anticipated to enable high sensitivity at temperatures above 300 °C. We report here mechanochemical activation experiments on 0.92Pb(Zn1/3Nb2/3)O3−0.08PbTiO3 that strongly suggest that mechanosynthesis is a good alternative for preparing high-sensitivity piezoelectric, low-tolerance perovskite materials. This is demonstrated by processing ceramics of the Pb(Zn1/3Nb2/3)O3−Pb(Fe1/2Nb1/2)O3−PbTiO3 and BiScO3−PbTiO3 systems from mechanosynthesized powders. Stabilization mechanisms are discussed, and associated effects are established.