Lignocellulosic biodiesel waste of Jatropha husk (JH) was used to develop ZnCl2 activated Jatropha husk carbon (ZAJHC). ZAJHC was applied as an adsorbent for the removal of methylene blue (MB) from contaminated water. Batch mode of adsorption experiments were carried out and the parameters investigated included agitation time, MB concentration (100–180 mg L−1) and adsorbent dose (25–200 mg/50 mL). The adsorption of MB reached equilibrium at 120 min for 100 mg L−1, 140 min for 120 mg L−1 and 160 min for other concentrations tested. Based on the Langmuir isotherm, the monolayer adsorption capacity (Q0) was found to be 500 mg g−1. The kinetic data were also fitted to the pseudo first-order, second-order and intraparticle diffusion models, and the experimental data followed closely the pseudo first-order kinetic model. Thermodynamic parameters such as standard enthalpy (ΔH° 3.86 J mol−1K−1), standard entropy (ΔS° 65.86 J mol−1K−1) and standard free energy (ΔG°) indicated the spontaneous nature of MB adsorption by ZAJHC. The adsorption was found to be endothermic in nature. Alkaline pH was favourable for the adsorption of MB. The pH effect and desorption studies suggest that ion-exchange might be the possible mechanism governing the adsorption process.