An intermediate-band (IB) semiconductor CuGa1−xCrxS2 was investigated by the self-consistent many-body GW approach (scGW) and further confirmed by the experimental results. The Cr dopant introduced a partially occupied IB, and the density-of-states analysis indicates the electron transfer between the impurities and host lattice would suppress the non-radiative recombination. The CuGa1−xCrxS2 was synthesized by a high-temperature solid-state reaction and the X-ray photoelectron spectroscopy (XPS) indicated the presence of Cr3+. Due to the Cr dopant, two additional absorption responses were directly observed in the UV–Vis–NIR absorption spectrum. The further photocatalytic investigations verified the IB absorptions could produce highly mobile electrons and holes to degrade dyes. This material leads to lower-energy photon absorption, which could be a promising candidate for the high-efficiency solar cells.