Materials with different combinations of piezoelectric and flexoelectric properties offer multifunctionality and versatility in terms of modes of operation in sensing, actuation, energy conversion, and energy harvesting. We explore a microscopic mechanism for tailoring the macroscopic electrical output of polymer-metal particle composites, which takes advantage of the heterogeneity-induced enhancement of and the interactions between stress fields and strain gradient fields at the microstructural level. The study focuses on using microscopic inclusions, such as embedded particles and voids, to manipulate the activation, interaction, and relative contributions of the piezoelectric and flexoelectric effects under different modes of mechanical excitation, including uniaxial compression and flexural bending. The material system studied is P(VDF-TrFE)/nAl, as P(VDF-TrFE) exhibits both piezoelectric and flexoelectric behaviors and nAl particles have significantly higher elastic stiffness than the polymer. A parametric study is carried out by varying the relative stiffness (i.e., Young’s modulus) of the particles. The induced electrical responses of the composite material under macroscopic compression and bending are quantified using the effective piezoelectric constant and the effective flexoelectric coefficient, respectively. The framework of analysis tracks the coupled mechanical-electrical effects. Systematic comparisons are made with the corresponding coefficients of the homogeneous P(VDF-TrFE) polymer to demonstrate the microstructural effects and cross-influence between the piezoelectric and flexoelectric contributions. Analyses reveal that significant microstructural effects exist to enable tailoring of the overall electromechanical response of the composite material by varying the volume fractions of the particles and voids.