While autologous transplants are the traditional standard intervention for non-healing bone defect regeneration, it carries many risks and limitations. Regenerative composite biomaterials are promising alternatives to conventional autograft and allograft implants. This research study seeks to overcome these challenges by creating a biodegradable novel 3D biomaterial scaffold that mimics native bone's structural and physiological properties. Scaffolds composed of magnesium phosphate (MgP) doped with copper oxide (CuO) in proportions (3, 5, or 7 %^w/_w) that were homogenously distributed in alginate (Alg) polymer matrix for the repair of calvarial bone defects in a rat model. The scaffolds were fabricated using a 3D bioprinting technique, and their physical properties were characterized through XRD, FTIR, and mechanical strength assessments. The bioactivity of the scaffolds was evaluated in vitro for biomineralization and cytotoxicity, revealing high biomineralization and cell viability. Female rats were used for the in vivo experiment; the defects were examined microscopically, histologically, CT imaging, and osteocalcin alongside procollagen PIIINP in serum. The in vivo study demonstrates high efficacy in promoting bone regeneration, and the results confirmed enhanced healing in the calvarial defect model. The incorporation of CuO not only improved the mechanical properties but also exhibited angiogenic effects, fostering an environment conducive to bone healing. Our results showed that the Alg-MgP-CuO scaffolds have great promise for bone tissue engineering (BTE) applications and repair, especially at the 7 wt% doping level.