Cu–chitosan nanoparticles were synthesized and evaluated for their growth promotory and antifungal efficacy in tomato (Solanum lycopersicum Mill). Physico-chemical characterization of the developed Cu–chitosan nanoparticles was carried out by DLS, FTIR, TEM, SEM-EDS and AAS. The study highlighted the stability and porous nature of Cu–chitosan nanoparticles. Laboratory synthesized nanoparticles showed substantial growth promotory effect on tomato seed germination, seedling length, fresh and dry weight at 0.08, 0.10 and 0.12% level. At 0.12% concentration these nanoparticles caused 70.5 and 73.5% inhibition of mycelia growth and 61.5 and 83.0% inhibition of spore germination in Alternaria solani and Fusarium oxysporum, respectively, in an in vitro model. In pot experiments, 0.12% concentration of Cu–chitosan nanoparticles was found most effective in percentage efficacy of disease control (PEDC) in tomato plants with the values of 87.7% in early blight and 61.1% in Fusarium wilt. The overall results confirm the significant growth promotory as well as antifungal capabilities of Cu–chitosan nanoparticles. Our model demonstrated the synthesis of Cu–chitosan nanoparticles and open up the possibility to use against fungal disease at field level. Further, developed porous nanomaterials could be exploited for delivery of agrochemicals.