CuSbSe2 appears to be a promising absorber material for thin-film solar cells due to its attractive optical and electrical properties, as well as earth-abundant, low-cost, and low-toxic constituent elements. However, no systematic study on the fundamental properties of CuSbSe2 has been reported, such as defect physics, material, optical, and electrical properties, which are highly relevant for photovoltaic application. First, using density functional theory calculations, CuSbSe2 is shown to have benign defect properties, i.e., free of recombination-center defects, and flexible defect and carrier concentration which can be tuned through the control of growth condition. Next, systematic material, optical, and electrical characterizations uncover many unexplored fundamental properties of CuSbSe2 including band position, temperature-dependent band gap energy, Raman spectrum, and so on, thus providing a solid foundation for further photovoltaic research. Finally, a prototype CuSbSe2-based thin film solar cell is fabricated by a hydrazine solution process. The systematic theoretical and experimental investigation, combined with the preliminary efficiency, confirms the great potential of CuSbSe2 for thin-film solar cell applications. Systematic theoretical and experimental investigations on CuSbSe2, combined with the preliminary efficiency of 1.32%, demonstrate that this material could be used as the absorber layer for cost-effective and environmentally friendly thin-film solar cells, due to its benign defect properties, attractive material, optical and electrical properties, as well as low-toxic, low-cost, and earth-abundant constituents.