This study assessed the effectiveness of Olive Leaf Biomass (OLB) and Sulfuric Acid-Treated Olive Leaf Biomass (SATOLB) in removing Methylene Blue (MB) from water. Sulfuric acid was used to activate SATOLB, resulting in improved adsorption effectiveness. The optimal removal of MB for both materials was observed at pH 6. SATOLB demonstrated an improved efficiency compared to OLB by achieving a 75% removal of MB within a timeframe of 8 min, surpassing OLB’s 36% removal rate. The pseudo-second-order model accurately characterizes the adsorption kinetics, suggesting chemisorption. The SATOLB and OLB phenomena can be accurately characterized by the Langmuir and Freundlich isotherms, respectively. These isotherms provide insights into the adsorption processes, indicating whether monolayer or multilayer adsorption is occurring. The process exhibited endothermicity and spontaneity, which were influenced by intraparticle diffusion, chemical interactions, and external mass transfer. The study suggests that SATOLB shows promise as an eco-friendly candidate for wastewater treatment.