Abstract: Graphene nanoplatelet (GNP)-reinforced metal matrix composites (MMCs) represent a groundbreaking group of lightweight structural materials, offering exceptional combinations of strength, toughness, and multifunctionality that are critical for next-generation applications. Graphene imparts exceptional properties that significantly enhance the performance of lightweight alloys such as aluminum and magnesium. The review first examines the ex-situ incorporation of GNPs into metal matrices and their effects on alloy solidification and mechanical properties based on process parameters, volume fraction, and matrix material. It then highlights two emerging in-situ strategies, including the Covetic process, which employs electrically assisted processing (EAP) to synthesize graphene within metallic melts, and CO₂ bubbling in magnesium alloys to form carbon-metal (C-M) bonds. Particular emphasis is placed on mechanisms of C-M bonding, dispersion challenges, and interfacial bonding between the metallic matrices and graphene. This review emphasizes the potential of graphene-reinforced MMCs across industries and identifies the persistent barriers to process upscaling.