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High‐power piezoelectric applications are predicted to share approximately one‐third of the lead‐free piezoelectric ceramic market in 2024 with alkaline niobates as the primary competitor. To suppress self‐heating in high‐power devices due to mechanical loss when driven by large electric fields, piezoelectric hardening to restrict domain wall motion is required. In the present work, highly effective piezoelectric hardening via coherent plate‐like precipitates in a model system of the (Li,Na)NbO₃ (LNN) solid solution delivers a reduction in losses, quantified as an electromechanical quality factor, by a factor of ten. Various thermal aging schemes are demonstrated to control the average size, number density, and location of the precipitates. The established properties are correlated with a detailed determination of short‐ and long‐range atomic structure by X‐ray diffraction and pair distribution function analysis, respectively, as well as microstructure determined by transmission electron microscopy. The impact of microstructure with precipitates on both small‐ and large‐field properties is also established. These results pave the way to implement precipitate hardening in piezoelectric materials, analogous to precipitate hardening in metals, broadening their use cases in applications.