AbstractLead in drinking water is a metabolic poison that causes mental retardation, temporary cerebral damage, and reproductive problems. Chemical precipitation, membrane technology, and ion exchange are some of the expensive and extravagant techniques used to eradicate lead from water. The process of accumulating heavy metals from wastewater using biological materials is referred to as biosorption. In this study, biosorption is examined using three biomasses obtained from Foeniculum vulgare (fennel), that is, its seeds, leaves, and stem, to treat lead-contaminated water. Physicochemical parameters, such as initial concentration of lead (II), contact time, biomass quantity, and pH of the solution are assessed. The optimum contact time to achieve equilibrium is found to be 45 min. The optimum biosorbent dosage, pH, and initial metal concentration are found to be 3.34 g/L, 6.4, and 1 mg/L, respectively. Langmuir, Freundlich, and Temkin models are used for modeling adsorption equilibrium isotherms. The Freundlich model provides the best fit for the biosorption process, with a correlation coefficient R2 greater than 0.999 for all three biosorbents. Adsorption kinetics can be described using pseudo first- and second-order kinetic models. The experimental data fit better with the pseudo second-order kinetic model, as the deviations in the experimental and calculated values of biosorption capacities at the time of equilibrium are 5.02%, 4.15%, and 4.66%, respectively, for Foeniculum vulgare seeds, leaves, and stem as biomasses. The process is found to be exothermic and spontaneous, as indicated with a negative change of Gibbs energy value of −1.958, −3.224, and −2.608 KJ mol−1, respectively, for fennel seeds, leaves, and stem. The study shows that the powdered form of Foeniculum vulgare seeds, leaves, and stem is a moderately effective, feasible, and economical adsorbent for the removal of lead from water.