Volumetric muscle loss remains a significant clinical challenge due to limited graft availability and insufficient bioactivity. This study introduces bioactive bioinks composed of magnesium peroxide (MgO2) integrated into a hydrogel system based on thiolated (GtnSH) and maleimide-conjugated gelatin (GtnMI). The GtnSH/GtnMI/MgO2 bioinks were fabricated in situvia a thiol-ene reaction and MgO2-mediated disulfide bond formation, ensuring long-term magnesium ion incorporation. In vitro evaluations demonstrated excellent cytocompatibility and substantial upregulation of myogenic markers in encapsulated C2C12 myoblasts. In vivo, the 3D-bioprinted constructs facilitated muscle mass restoration by fostering an immune-favorable microenvironment. Importantly, they mitigated M1 macrophage polarization and reduced the activities of CD4+ and CD8+ T cells. These findings suggest that the GtnSH/GtnMI/MgO2 hydrogel constitutes a promising bioactive platform for advanced skeletal muscle regeneration.