Powder-bed fusion additive manufacturing (PBF-AM) technology has attracted substantial attention as an innovative method for rapidly and accurately fabricating complex, near-net-shape metallic components. While stainless steels produced via PBF-AM generally exhibit excellent mechanical properties at room temperature—due to the unique microstructural characteristics formed under steep thermal gradients and rapid cooling rates—their behavior at elevated temperatures remains underexplored. Here, a comprehensive study is conducted on the mechanical behavior of a fine equiaxed-grained 316L stainless steel (SS) additively manufactured by electron-beam powder bed fusion (EB-PBF) method. Over temperatures ranging from room temperature to 600 °C, EB-PBF 316L SS exhibits isotropic behavior and remarkable tensile properties (yield strength, ultimate tensile strength, and elongation) compared to conventional wrought 316L SS. Grain boundary strengthening and dispersion strengthening from amorphous silicon oxide nanoparticles collectively account for the reasonably good room-temperature yield strength, and these particles continue to impede dislocation motion at elevated temperatures. The temperature-dependent mechanical properties of EB-PBF 316L SS are examined in the context of evolving deformation mechanisms and microstructural characteristics. Above 200 °C, deformation twinning is suppressed, whereas dynamic strain aging (DSA) arises between 300 °C and 600 °C. Despite the presence of DSA, no abrupt drop in ductility is observed, which is attributed to the formation of sub-grains in strain-free state through dynamic recrystallization during plastic deformation.