Abstract: During the operation of electronic devices, a considerable amount of heat and electromagnetic radiation is emitted. Therefore, the investigation of materials with electromagnetic shielding and thermal management abilities has significant importance. Hybrid materials of three-dimensional graphene networks containing both carbon nanotubes (CNTs) and SiC whiskers (3D graphene-CNT-SiC) were synthesized. Using an aqueous-phase reduction method for the self-assembly of the graphene oxide, a three-dimensional porous graphene structure was fabricated. SiC whiskers, inserted between the graphene layers, formed a framework for longitudinal thermal conduction, while CNTs attached to the SiC surface, created a dendritic structure that increased the bonding between the SiC whiskers and graphene, improving dielectric loss and thermal conductivity. It was found that the thermal conductivity of the hybrid material reached 123 W·m^–1·K^–1, with a shielding effectiveness of 29.3 dB when the SiC addition was 2%. This result indicates that 3D Graphene-CNT-SiC has excellent thermal conductivity and electromagnetic shielding performance.