Photocatalytic decarboxylation of fatty acids derived from biomass is considered a sustainable approach for alkane production. In this study, a series of NiS2 co-catalyst-modified TiO2 (NiS2/TiO2) composites were successfully synthesized and employed for the photocatalytic decarboxylation of fatty acids. Under mild conditions, the optimized NiS2/TiO2 composite exhibited conversion of 60.2% and selectivity of 72.6% for converting chondritic acid to pentadecane, which was 6.56 times to single TiO2. The incorporation of the co-catalyst led to red shift of the absorption edge, and decrease in photoluminescence (PL) intensity, indicating enhanced light absorption and efficient separation of photogenerated charge in NiS2/TiO2. The lower work function of NiS2 compared with TiO2 and the differential charge density indicated that electrons tended to migrate from the S-atom to the O-atom, thus creating a built-in electric field that accelerated the reaction. The study on biofuel synthesized from biomass offered insights that can help mitigate future energy crises.