Lattice-strained Bi2S3 with 3D hierarchical structures are prepared through a top-down route by a topotactic transformation. High-resolution transmission electron microscopy and X-ray diffraction (XRD) confirm the lattice spacing is expanded by prolonged sulfuration. Performance studies demonstrate that Bi2S3 with the largest lattice expansion (Bi2S3-9.7%, where 9.7% represents the lattice expansion) exhibits a greater electrocatalytic hydrogen evolution reaction (HER) activity compared to Bi2S3 and Bi2S3-3.2%. Density functional theory calculations reveal the expansion of the lattice spacing reduces the bandwidth and upshifts the band center of the Bi 3d orbits, facilitating electron exchange with the S 2p orbits. The resultant intrinsic electronic configuration exhibits favorable H* adsorption kinetics and a reduced energy barrier for water dissociation in hydrogen evolution. Operando Raman and post-mortem characterizations using XRD and X-ray photoelectron spectroscopy reveal the generation of pseudo-amorphous Bi at the edge of Bi2S3 nanorods of the sample with lattice strain during HER, yielding Bi2S3-9.7%-A. It is worth noting when Bi2S3-9.7%-A is assembled as a positive electrode in an asymmetric supercapacitor, its performance is greatly superior to that of the same device formed using pristine Bi2S3-9.7%. The as-prepared Bi2S3-9.7%-A//activated carbon asymmetric supercapacitor achieves a high specific capacitance of 307.4 F g−1 at 1 A g−1, exhibiting high retention of 84.1% after 10 000 cycles.