The behaviour of a bulk lead zirconate titanate ceramic has been characterised under combined high stress and high electric field. The electrical response of the sample was monitored, and Digital Image Correlation (DIC) was used to characterise the strain field at the surface of the sample. The DIC technique allows both longitudinal and transverse strains to be measured simultaneously. The results showed that a compressive stress of 25 MPa increases the susceptibility by 128% and the longitudinal piezoelectric coefficient by 47%. A further increase of stress has reversed this trend and under a 500 MPa compression, the susceptibility has fallen by 71% and the longitudinal piezoelectric coefficient by 98% compared to the unstressed case. The analysis of the ferroelastic contribution revealed that this decrease is explained by a saturation of the ferroelastic switching, beginning at the coercive field. The material volume change during loading was computed using the DIC results. It was found that a negligible piezoelectric activity remains at 500 MPa while ferroelastic switching still occurs and is reversible. This work shows that it is possible to obtain quantitative insights into the physical mechanisms underlying the macroscopic behaviour of ferroelectrics using the DIC technique without requiring the use of local investigation technique.