Background and Objectives: Composite systems based on molecular ferroelectrics and metallic inclusions attract considerable attention due to the possibility of controlled modification of phase transition parameters and dielectric response. In contrast to extensively studied inorganic ferroelectric–metal composites, the influence of metallic microparticles on organic ferroelectrics remains insufficiently explored. Diisopropylammonium bromide is a promising organic ferroelectric characterized by a first-order phase transition and a relatively high spontaneous polarization. The aim of this work is to investigate the effect of 2 vol.% copper microparticles on the dielectric and thermal properties, Curie temperature, and phase transition behavior of diisopropylammonium bromide-based composites. Materials and Methods: Composite samples were prepared by mechanical mixing of diisopropylammonium bromide powder with Cu microparticles (≈1 μm) followed by pressing into pellets. Morphology and elemental distribution were examined by scanning electron microscopy. Dielectric permittivity was measured in the temperature range 30–170°C. Phase transitions were analyzed using differential thermal analysis. Results: Pure diisopropylammonium bromide exhibits a first-order ferroelectric–paraelectric transition at 426 K with thermal hysteresis. In the composite, a pronounced decrease in the Curie temperature and splitting of the phase transition into two peaks (≈120 and 133°C) have been observed. The splitting is attributed to microstructural heterogeneity and the formation of diisopropylammonium bromide regions with different interfacial boundary conditions in contact with Cu particles. Conclusion: Copper microparticles significantly modify the thermodynamic potential of the ferroelectric matrix due to interfacial screening and surface energy contributions. The observed reduction and splitting of the phase transition are consistent with the Landau–Ginzburg.