The clean conversion of carbon dioxide and water to a single multicarbon product and O2 using sunlight via photocatalysis without the assistance of organic additives or electricity remains an unresolved challenge. Here we report a bio-abiotic hybrid system with the nonphotosynthetic, CO2-fixing acetogenic bacterium, Sporomusa ovata (S. ovata) grown on a scalable and cost-effective photocatalyst sheet consisting of a pair of particulate semiconductors (La and Rh co-doped SrTiO3 (SrTiO3:La,Rh) and Mo-doped BiVO4 (BiVO4:Mo)). The biohybrid effectively produces acetate (CH3COO–) and oxygen (O2) using only sunlight, CO2 and H2O, achieving a solar-to-acetate conversion efficiency of 0.7%. The photocatalyst sheet oxidises water to O2 and provides electrons and hydrogen (H2) to S. ovata for the selective synthesis of CH3COO– from CO2. To demonstrate the utility in a closed carbon cycle, the solar-generated acetate was used directly as feedstock in a bioelectrochemical system for electricity generation. These semi-biological systems thus offer a promising strategy for sustainably and cleanly fixing CO2 and closing the carbon cycle.