In this study, the effect of Poisson’s ratio on the electrical characteristics and dynamic response of sandwich beams with piezoelectric patches for energy harvesting purposes is investigated. The sandwich beam consists of a homogeneous core and composite face sheets, with one of the layers being piezoelectric. The higher-order shear deformation theory and through-the-thickness deformation are considered for the core. The finite element model is implemented based on one-dimensional, three-node elements with Lagrangian and Hermitian shape functions. Parametric studies are conducted to determine the influence of Poisson’s ratio on the natural frequencies of short-circuit and open-circuit conditions, voltage, and displacement amplitude of the beam under resonant excitation frequency. According to the results, the effect of neglecting Poisson’s ratio on the natural frequencies and displacement at zero excitation frequency is insignificant for orthogonal fiber orientation, but becomes pronounced for skewed fibers. In contrast, when examining the voltage and displacement amplitude of the beam, the error is quite significant for both orthogonal and skewed fibers, and cannot be overlooked. Furthermore, the largest error occurs at an approximately 36-degree fiber angle. Additionally, the asymmetry in the positioning of the piezoelectric patches at orthogonal angles can result in a greater error than in the symmetric configuration or their full coverage. Finally, it was observed that for the beam with a length-to-width ratio (L/b) of approximately 30 or higher, the results of the present model converge with the three-dimensional model results from COMSOL software.