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Quadruple perovskite oxides have received extensive attention in electronics and catalysis, owing to their cation-ordering structure and intriguing physical properties. However, their repertoires still remain limited. In particular, piezoelectricity from quadruple perovskites has been rarely reported due to the frustrated symmetry-breaking transition in A-site-ordered perovskite structures, disabling their piezoelectric applications. Herein, we report a feasible strategy to achieve piezoelectricity in CaCu3Ti4O12 (CCTO) quadruple perovskite via cation defect engineering, specifically through a thermal-driven selective cation exsolution strategy to introduce Cu vacancies. The introduction of Cu point defects in CCTO locally destabilizes the constrained tilted TiO6 octahedra framework, relaxing the octahedral tilting and inducing structural heterogeneity which, in turn, disrupts the high symmetry of the pristine cubic phase. As a result, the defective CCTO with localized asymmetry exhibits intense polarization and a robust piezoelectricity of 7 pC N–1. The created piezoelectricity is further validated by its application as a piezo-photocatalyst, enabling efficient charge separation and transfer with a 2.5-times increment in the lifetime of photoexcitations. This enhancement leads to a 3.86- and 31-fold increase in the production of hydrogen peroxide and reactive oxygen species compared with individual piezocatalysis and photocatalysis, respectively. This study establishes a pathway to engineer piezoelectricity in quadruple perovskites, potentially unlocking a wide range of applications in modern microelectronics beyond the demonstrated piezo-photocatalysis.