Magnetoelectricity enables a solid-state material to generate electricity under magnetic fields. Most magnetoelectric composites are developed through a strain-mediated route by coupling piezoelectric and magnetostrictive phases. However, the limited availability of high-performance magnetostrictive components has become a constraint for the development of novel magnetoelectric materials. Here, we demonstrate that nanostructured composites of magnetic and pyroelectric materials can generate electrical output, a phenomenon we refer to as the magnetopyroelectric (MPE) effect, which is analogous to the magnetoelectric effect in strain-mediated composite multiferroics. Our composite consists of magnetic iron oxide nanoparticles (IONPs) dispersed in a ferroelectric (and also pyroelectric) poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) matrix. Under a high-frequency low-magnitude alternating magnetic field, the IONPs generate heat through hysteresis loss, which stimulates the depolarization process of the pyroelectric polymer. This magnetopyroelectric approach creates a new opportunity to develop magnetoelectric materials for a wide range of applications.