This study investigates the pyrolysis and adsorption properties of biochar derived from coconut shell (BC-CS), rice husk (BC-RH), and cow manure (BC-CM) under varying thermal treatment conditions. Biochar samples were produced at 800 °C with residence times ranging from 0 to 60 min. Their characteristics were analyzed using their Brunauer–Emmett–Teller (BET) surface area, total pore volume, and pore diameter measurements. BC-CM exhibited the highest BET surface area of 263.3 m2/g and a total pore volume of 0.164 cm3/g, while BC-RH and BC-CS showed maximum BET surface areas of 220.62 m2/g and 197.38 m2/g, respectively. Nitrogen adsorption–desorption isotherms revealed distinct microporous and mesoporous structures, with BC-CM demonstrating superior adsorption capacity across all relative pressures. The adsorption kinetics of methylene blue (MB) were examined at initial concentrations of 1 ppm, 5 ppm, and 10 ppm, with varying biochar doses (0.1 g, 0.3 g, and 0.5 g). The results showed that the adsorption rate constant (k) decreased with higher initial MB concentrations, while the equilibrium adsorption capacity (qe) increased. BC-CM achieved the highest qe of 2.18 mg/g at 10 ppm and a 0.5 g dose, followed by BC-RH-800-45 (1.145 mg/g) and BC-CS (0.340 mg/g). The adsorption process was well described by a pseudo-second-order kinetic model, indicating chemisorption as the dominant mechanism. Increasing biochar doses improved MB removal efficiency, highlighting the dose-dependent nature of adsorption. These findings underscore the importance of optimizing pyrolysis parameters to enhance biochar’s adsorption performance and identify key factors influencing its effectiveness in environmental applications.