This study investigated the effect of pyrolysis temperature on the adsorption performance of biochar derived from Jordanian olive mill solid waste (OMSW) for methylene blue (MB) removal. Batch adsorption experiments were conducted under varying adsorbent dosages, pH values, contact times, initial MB concentrations, and temperatures using biochars produced at 400, 500, 600, and 700 °C. MB adsorption capacity decreased with increasing adsorbent dosage, with the highest value (12 mg/g) achieved at 1 g/L using the 400 °C biochar, while biochars produced at 500 and 700 °C showed the lowest MB affinity. Adsorption was enhanced under alkaline conditions, with optimal pH values of 8 and 10 for the 400 and 600 °C biochars, respectively. Kinetic analysis indicated that MB adsorption on the 400 °C biochar followed pseudo-first-order and Elovich models, suggesting combined physisorption and chemisorption, whereas adsorption on the 600 °C biochar was best described by the pseudo-second-order model, indicating dominant chemisorption. Isotherm analysis showed that adsorption on the 400 °C biochar fitted the Langmuir, Freundlich, and Temkin models, reflecting mixed adsorption behaviour, while the 600 °C biochar followed only the Langmuir model, confirming monolayer adsorption on a homogeneous surface. FTIR results revealed that the 400 °C biochar contained more oxygenated functional groups, whereas the 600 °C biochar was more carbonized and aromatic. Thermodynamic analysis demonstrated that MB adsorption was endothermic, favouring higher temperatures. Overall, the findings support the sustainable valorisation of Jordanian OMSW into effective biochar for aquatic contaminant removal.