Sn–58Bi specimens produced through severe plastic deformation (SPD) typically exhibit excellent superplastic properties. However, the dimensions of SPD-prepared specimens are limited, and the process involves complex multistep procedures, which limit their practical engineering applications. Therefore, developing alternative fabrication techniques with greater flexibility and scalability is particularly important. In this study, a Sn–58Bi alloy was fabricated using laser powder bed fusion (LPBF). After the processing parameters were optimized, Sn–58Bi with remarkable superplasticity was successfully fabricated via additive manufacturing for the first time. Tensile tests revealed elongations to failure of 740% at room temperature (298 K) and 1395.5% at 353 K. In situ scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses indicated that grain boundary sliding (GBS) and phase boundary sliding (PBS), which are predominantly influenced by diffusion processes, were the primary mechanisms of superplastic deformation in the LPBF-fabricated Sn–58Bi alloy. This study provides a new strategy for enhancing alloy ductility through LPBF and offers theoretical insights into the additive manufacturing of superplastic polycrystalline alloys.