In the current study, Elettaria cardamomum (Ec) seed extract–assisted zinc oxide nanoparticles (ZnO NPs) were synthesized by a secure co-precipitation method and characterized through UV–vis, XRD, FTIR, SEM and TEM. The surface plasmon resonance of Ec-ZnO NPs was distinguished at 373 nm. The XRD pattern authenticates the crystalline nature and matches with JCPDS file No. 36-1451. The result acquired from the FTIR spectrum conveyed the potential biomolecules that take place in the Ec-ZnO NPs by sharp express peaks at 3472.30, 1416.81, 1573.95, 1557.02, and 848.25 Cm−1. SEM and TEM images make known the homogenous spherical form and average size (18.72 nm) of Ec-ZnO NPs, respectively. The Ec-ZnO NPs have better antioxidant activity at 100 μg/ml concentration than Ec seed extract. Additionally, the Ec-ZnO NPs were encompassed with enhanced antibiofilm activity at 100 μg/ml concentration against four different bacteria Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus vulgaris. Among them, Gram-negative bacteria were more susceptible to Ec-ZnO NPs. Moreover, when compared to Ec seed extract, the Ec-ZnO NPs was highly potential agent against Aedes aegypti (LC50 = 13.27 μg/ml, LC90 = 25.36 μg/ml) and Culex tritaeniorhynchus (LC50 = 15.09 μg/ml, LC90 = 29.70 μg/ml). Compare to Cx. tritaeniorhynchus, Ae. aegypti was more susceptible to Ec-ZnO NPs. Thus, the Ec-ZnO NPs can probably utilize to reduce the bacterial biofilm in the discipline of biomedical and pharmaceutics and as well as remarkable larvicidal agent to the constraint of mosquito vectors.