A copper sulfide precursor of the general formula Cu(C13H9O2NCl)2(H2O)2 {C13H9O2NCl = 2-(2-chlorophenylamino)benzoate} was synthesized and routinely characterized regarding its CHN content, solution molar conductivity, powder X-ray diffraction (PXRD) pattern, magnetic moment and IR spectroscopic data. Copper sulfide Cu1.90S nanoparticles (CSNPs) were hydrothermally grown from this precursor and thiourea. The NPs were characterized by means of elemental analyses, PXRD and transmission electron microscopy (TEM). Brunauer–Emmett–Teller (BET) surface area measurements assigned mesoporous structure and an average pore diameter of 14.342 nm for the as-prepared NPs. The microbial resistance against common antimicrobial agents and the development of new microbial strains are urging factors for finding alternate potent antimicrobial agents. The as-prepared CSNPs may conquer plant diseases, as they exhibited antifungal efficiency against eleven phytopathogenic fungal isolates with Fusarium oxysporum growth reduction reaching 52.63%. Additionally, these NPs strongly inhibited the cellulase enzyme activity produced by Fusarium camptoceras by 51.54% at 30 °C and also inhibited the enzyme activity produced by Trichoderma harzianum by 55.4% at 40 °C leading to promising usefulness of the as prepared CSNPs in improving the quality and quantity of agricultural crops and protecting them from several plant diseases.