We describe a new organic peroxide-based injectable biomaterial that was prepared by using benzoylperoxide and LAPONITE® incorporated into an alginate hydrogel (BPO–AlgL). BPO–AlgL shows sustained release of O₂ over a period of 14 days and reduces the hypoxia-induced cell death. BPO–AlgL also promotes enhanced cell viability by providing sustained O₂ within the 3D AlgL scaffold. In addition, BPO–AlgL increases the O₂ level in the environment of the cells, which led to a decrease in the proliferation of malignant cells, while it also resulted in an increase in the viability of healthy fibroblast cells. Therefore, our new oxygen generating organic peroxide-based injectable 3D biomaterials have potential to contribute in the development of next generation advanced tissue engineering biomaterials.