The biggest contribution to the global warming phenomenon is a rise in carbon dioxide, which causes climate change. The need for a novel and low-cost composite catalyst to capture and convert CO₂ from the atmosphere into solar fuel is in high demand. Slag waste from a steel-making company is one of the low-cost raw materials. This slag was synthesized in this study using a solvothermal preparation technique to produce a steel slag nanocomposite catalyst. The chemical and elemental composition, morphology, crystallographic structure, and band gap were evaluated using EDX, SEM, TEM, FTIR, XRD, and UV-vis spectroscopy, respectively. The result reveals that the EAF-SSNC exhibited nanocomposite behavior with a band gap of 1.67eV. The prepared slag nanocomposite was utilized under a continuous flow photo-reactor for CO₂ reduction with water for the first time. The resulting product was analyzed using total organic carbon (TOC) analyzer and gas chromatography–mass spectrometry (GC-MS). Based on the gas chromatography analysis of the liquid products, it was revealed that CH3OH was the predominant product, whereas HCHO was the minor one. EAF-SSNC achieved 37mg/L TOC concentration in CO₂ reduction. This work showed that steel slag nanocomposites might be effectively used for CO₂ reduction and will reduce the overall cost of using pure chemicals.