To address the challenges associated with the weak affinity and difficult separation of biochar, we developed chitosan–biochar hydrogel beads (CBHBs) as an efficient solution for removing reactive brilliant blue (RBB KN-R) from wastewater. The adsorption behavior and mechanism of RBB KN-R onto CBHBs were extensively studied. Notably, the adsorption capacity of RBB KN-R showed pH-dependence, and the highest adsorption capacity was observed at pH 2. The adsorption process was well fitted with the pseudo-second-order kinetic model and the intraparticle diffusion model. Film diffusion and intraparticle diffusion were both responsible for the adsorption of RBB KN-R onto CBHBs. At 298.15 K, the maximum adsorption capacity qm was determined to be 140.74 mg/g, with higher temperatures favoring the adsorption process. A complex mechanism involving π–π interactions, electrostatic attraction, hydrophobic interaction, and hydrogen bonding was found to contribute to the overall adsorption process. The experimental data discovered the coexisting substances and elevated ionic strength hindered the adsorption capacity. Significantly, after three cycles of adsorption–desorption, the CBHBs maintained an adsorption capacity above 95% for RBB KN-R. These promising results imply that CBHBs are a durable and cost-effective adsorbent for efficient removal of dyes from wastewater.