Achieving synergy between mechanical and biological performance has long been a challenge in developing silicon nitride (Si₃N₄) as a bone regeneration implant material. In this study, a nanostructured graphene-toughened Si₃N₄ composite (Si₃N₄–G) was prepared, and the mechanical and biological properties of the resulting Si₃N₄–G composite were compared with those of Si₃N₄ ceramics without graphene addition. The incorporation of nanostructured graphene substantially improves the mechanical properties of Si₃N₄. Furthermore, the nanoscale thickness of graphene enhances antibacterial activity through a “cutting” effect, while its high specific surface area promotes cell adhesion, activating mechanosensitive pathways linked to osteogenic differentiation. This work provides new insights into the potential applications of Si₃N₄-based bio-ceramics in bone tissue engineering.