Yolk–shell nanocages possessing complex internal structure and excellent structural tenability are advantageous for the preparation of advanced catalysts. Due to outstanding features such as superior electrical, magnetic, optical and catalytic properties, non-noble metal materials with hollow nanostructures have been considered potential substitutes for highly active and stable abundant noble-metal electrocatalysts. In this study, the as-prepared CoS₂–C@CoS₂ yolk–shell nanocages were applied in both dye-sensitized solar cells (DSSCs) and hydrogen evolution reactions (HERs). Due to the remarkable structural features and advantageous chemical compositions, CoS₂–C@CoS₂ yolk–shell nanocages comprising tiny crystals possessed large surface area (161 m² g⁻¹), well-defined interior voids, excellent conductivity and high catalytic activity. The DSSC with CoS₂–C@CoS₂ achieved a high power conversion efficiency (PCE) of 9.32% under AM 1.5 G irradiation, and it outperformed the DSSC with Pt (8.24%). Besides, CoS₂–C@CoS₂ as a kind of HER catalyst also exhibited a low onset overpotential of 19.0 mV, small Tafel slope of 51.9 mV dec⁻¹ and low overpotential of 79.1 mV at a current density of 10 mA cm⁻² under acidic conditions (0.5 M H₂SO₄).