Conversion of agricultural biomass waste to value-added biochar based catalysts receives tremendous interests because it falls into the scope of resource recycle concept. In this work, a magnetic nitrogen doped biochar-supported CoFe2O4 composite (MNBC) was synthesized by using rice straw, an abundant agricultural waste as the precursor. The prepared catalyst exhibited excellent performance in catalytic degradation of metolachlor (MET), a broad-spectrum chloroacetanilide herbicide, by coupling with peroxymonosulfate (PMS). The pyrolysis temperature played a significant role in the activity of the resultant catalysts. Among others, MNBC 800 catalyst performed the best stability and reusability. In-situ (EPR) analysis revealed that SO4 center dot-, center dot OH and O-1(2) participated into the degradation process and the SO4 center dot- was the major contributor. The degradation was promoted at neutral and weak basic conditions, whilst significantly inhibited at strong basic condition (pH = 11). Eleven degradation intermediates were successfully identified through liquid chromatography - quadrupole time-of-flight - mass spectrometer (LC-Q-TOF-MS). The degradation mainly occurred via hydroxylation, dechlorination, and dealkylation reactions. Additionally, though the degradation was greatly inhibited in real wastewater, it was not remarkably influenced in river and groundwater, implying its applicability in river/groundwater remediation. Eventually, the easy separation and low toxicity make the catalyst promising for the degradation of MET from several aquatic systems. This study would pave the way to the catalytic degradations of organic pollutants by low-cost biochar based catalysts.