Tremendous impacts are usually made by the synthesis method and consolidation technique on microstructure and interface of graphene/Al composites. In the present work, an in situ gel-precursor decomposition route is proposed for the one-step synthesis of graphene nanosheet (GNS) decorated with Cu nanoparticles in the form of hybrid layers encapsulating Al grains (designated as GNS–Cu/Al). Consolidation is performed by spark plasma sintering (SPS) using markedly different sets of maximum temperature and maximum uniaxial pressure (400 °C/400 MPa or 500 °C/100 MPa). The powder and dense samples are investigated by several techniques including thermal analysis, X-ray diffraction and electron microscopy. The microhardness and elastic modulus of selected GNS–Cu/Al composites are investigated and related to the microstructure and preparation conditions. Results demonstrate that the interface structure is primarily determined by the roles of GNS–Cu hybrid layers and finely controlled by SPS conditions. This work paves a novel way to elucidate the evolutions of metal-decorated graphene hybrids in Al matrix composites.