The efficient activation of sodium percarbonate (SPC) is essential for degrading organic contaminants. Converting biomass into biochar as a multifunctional biocatalyst to accelerate oxidizer activation for water remediation has attracted much attention. In this study, we explored the performance of coconut shell biochar (CSBC) as a catalyst to activate SPC for degrading a model pollutant, rhodamine B (RhB). Optimal CSBC was synthesized via pyrolysis at 700°C for 4 h. In the CSBC/SPC system, the removal efficiency of RhB reached 96.11% within 4 h, which was much higher than that of the SPC system (7.76%). Quenching and electron paramagnetic resonance (EPR) spectroscopy results showed that hydroxyl radicals are crucial reactive oxygen species for RhB removal. Graphitization structures of the material, oxygen-containing functional groups, and persistent free radicals were the dominant factors controlling the activation of SPC by CSBC. Moreover, higher pH (11.72) enhanced the removal of RhB in the CSBC/SPC system; a 30% increase in removal rate was observed. However, anions Cl-, SO4 2-, and PO4 3- in water slightly inhibited the removal of RhB. This work provided a new method to activate SPC for the degradation of contaminants in water.