In our previous study, we developed Mg-matrix composites with bredigite as the reinforcing phase and achieved improved degradation resistance in comparison with Mg. However, the effects of materials processing method and process parameters on the mechanical behavior of the composites before and during degradation were still unknown. This research was aimed at determining the mechanical properties of Mg-bredigite composites prior to and during degradation. It was found that by optimizing the process parameters of Pressure Assisted Sintering (PAS), low-porosity Mg-bredigite composites with strong interfaces between homogeneously distributed bredigite particles and the Mg matrix could be fabricated. By reinforcing Mg with 20 vol% bredigite particles, the ultimate compressive strength and ductility of Mg increased by 67% and 111%, respectively. The in vitro degradation rate of the Mg-20% bredigite composite in a cell culture medium was 24 times lower than that of monolithic Mg. As a result of retarded degradation, the mechanical properties of the composite after 12 days of immersion in the cell culture medium were comparable to those of cortical bone. The encouraging results of this research warrant further investigations on the in vivo degradation behavior and mechanical properties of the composites.