Spent mushroom compost biochar (SMCB) was prepared by carbonization and tested for the removal of heavy metals (Zn(II), Cu(II), and Pb(II)) by adsorption. The sorption of heavy metals was evaluated by studying several factors, such as the initial solution pH, contact time, temperature, and individual and competitive adsorption. Kinetic and equilibrium studies were carried out to determine the mechanism involved during adsorption. The Weber-Morris model demonstrated the significance of intraparticle diffusion on the adsorption process. In addition, thermodynamic studies showed that the process is endothermic and favorable, with good affinity of metals to the biochar. At last, SMCB was used as the adsorbent in a continuous fixed-bed column. The breakthrough curve was obtained for each heavy metal, and Thomas and Clark models were fitted. When all three metals coexisted in solution, competitive adsorption took place in both batch and continuous systems, showing that Pb has higher affinity to SMCB than Cu and Zn.