Additive manufacturing using material extrusion (MEX) for metals has been available for years, but limited studies have been conducted on the fatigue strength of metal materials manufactured using this method. This study investigates the fatigue properties of austenitic stainless steel 316L manufactured using MEX, including the influence of severe shot peening (SSP) on reducing the impact of porosity. Samples were subjected to axial and flexural bending loading conditions, and the mechanical strength and microstructure of the material were investigated. The results of the study show that MEX-manufactured 316L exhibits improved material properties, including grain refinement and martensite transformation, compared to traditional sheet metal materials. Furthermore, SSP processing significantly enhanced both mechanical strength and fatigue life. The fatigue limit was over 60% greater compared to the as-built condition in bending loading, even exceeding the level of sheet metal materials in the low cycle range. This study demonstrates the potential of MEX as a viable additive manufacturing method for metal materials, particularly in applications where fatigue properties are critical. The results suggest that SSP can be an effective post-processing technique to reduce the impact of porosity and improve the fatigue properties of MEX-manufactured 316L.