In this study, poly(m-phenylenediamine)@ZnO (PmPDA@ZnO) nanocomposite was fabricated by in-situ chemical oxidative polymerization for the effective lead(II) removal from aqueous solutions. PmPDA@ZnO was characterized by several instrumental methods like FTIR, XRD, EDX, TGA, FESEM, TEM, zeta potential, and BET. The TEM images showed a core–shell-like structure for the PmPDA@ZnO nanocomposite. TGA results showed that the thermal stability of the PmPDA@ZnO nanocomposite was higher than the PmPDA. The maximum adsorption of lead (II) onto PmPDA@ZnO nanocomposite was obtained at pH 6, adsorbent dosage 60 mg, lead(II) ion concentration 90 mg/L, and agitation time 90 min. Langmuir and Freundlich's isotherm models were evaluated to simulate the lead(II) sorption via empirical data. Langmuir's model was in good agreement with empirical data with a maximum adsorption capacity (Qmax) of 77.51 mg/g. The kinetic data adsorption fitted best the pseudo-second-order model. The values of thermodynamic parameters of ΔS° and ΔH° were obtained 0.272 J/mol K, and 71.35 kJ/mol, respectively. The spontaneous and endothermic behavior of the adsorption process was confirmed by the negative and positive response of ΔG° and ΔH°, respectively. Moreover, the addition of coexisting cations e.g. cobalt (II), nickel (II), calcium (II), and copper (II) had no significant effect on the removal efficiency of lead(II). Adsorption–desorption studies showed that the PmPDA@ZnO nanocomposite can be remarkably regenerated and reused after three sequential runs without a significant decline in its adsorption performance. The antimicrobial activities of PmPDA@ZnO nanocomposite were evaluated against Escherichia coli and Staphylococcus aureus bacteria species. These results confirmed that the PmPDA@ZnO nanocomposite could be a good candidate for water decontamination.