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Abstract The pursuit of smaller, energy‐efficient devices drives the exploration of electromechanically active thin films (<1 µm) to enable micro‐ and nano‐electromechanical systems. While the electromechanical response of such films is limited by substrate‐induced mechanical clamping, large electromechanical responses in antiferroelectric and multilayer thin‐film heterostructures have garnered interest. Here, multilayer thin‐film heterostructures based on antiferroelectric PbHfO₃and ferroelectric PbHf_1‐xTi_xO₃overcome substrate clamping to produce electromechanical strains >4.5%. By varying the chemistry of the PbHf_1‐xTi_xO₃layer (x = 0.3‐0.6) it is possible to alter the threshold field for the antiferroelectric‐to‐ferroelectric phase transition, reducing the field required to induce the onset of large electromechanical response. Furthermore, varying the interface density (from 0.008 to 3.1 nm⁻¹) enhances the electrical‐breakdown field by >450%. Attaining the electromechanical strains does not necessitate creating a new material with unprecedented piezoelectric coefficients, but developing heterostructures capable of withstanding large fields, thus addressing traditional limitations of thin‐film piezoelectrics.