A simple cost-effective sono-chemical method was used for the synthesis of gCN/TeO2-ZnO ternary (2%, 5%, and 10%) nanocomposites, having crystallite size of 12 nm. FE-SEM and transmission electron microscopy images revealed the formation of core–shell type nanocomposites with an average size of 50 nm. Further, E. coli MTCC 443 strain is used as a model organism to study the antibacterial activity of the prepared nanocomposites, using disc diffusion method. Among all the concentrations, 2% gCN/TeO2-ZnO showed maximum zone of inhibition of 23 ± 0.10 mm and its antibacterial activity is like third-generation antibiotic cefotaxime. In addition, the prepared nanocomposites were used as nanofertilizer for the growth of gram seeds Chickpea (Cicer arietinum). The effect of nanocomposite concentration and its sterilising properties are studied on the rate of germination of Chickpea using both in vitro and in vivo studies (pot study). The root length of the gCN/TeO2-ZnO treated plants showed increase in seed germination (3.30 cm) compared to untreated plants (3.22 cm). In addition, enhancement in the shoot length about 28% is noticed in pot studies, compared to control batch samples. The accumulation of nanomaterial in plant roots was confirmed using SEM-EDX and ICP-MS. Finally, a 14-day experiment was conducted to ascertain the role of gCN/TeO2-ZnO in the controlled release of nutrients from the synthesised nanofertilizer. Owing to its excellent water holding capacity, sterilizing properties, and low toxicity this material can be used as a growth promoter in plants.