Abstract: In this work, nickel (Ni)@graphene nanoplatelet (GNP) nanohybrids were obtained via an interfacial reaction growth (IRG) method, and a series of poly(methyl methacrylate) (PMMA)/Ni@GNP composites were prepared by a solution mixing-ultrasonic dispersion-hot pressing technology. The influence of Ni@GNP on the electromagnetic interference (EMI) shielding, dielectric and thermal management behaviors of the composites was intensively investigated. The micro-capacitors formed using Ni@GNP as plates and PMMA as matrix significantly improved the dielectric properties of the composites. Enhancement on thermal conduction and EMI properties of PMMA composites with increasing Ni@GNP content could be ascribed to the unique structure of Ni@GNP, and it was the filler interconnection network that rendered the composites desirable thermally conductive and thermomechanical properties. The current study provides a facile way of fabricating polymeric composites with satisfactory thermal conductivity and high-performance electromagnetic shielding, the obtained polymer composites display highly promising applications in the thermal management and EMI shielding of electronic devices.