Novel nanocomposites of Ag₃PO₄/Bi₂WO6/MWCNTs were prepared via a facile hydrothermal method and in-situ precipitation without the addition of any spherical template. The composites exhibited excellent catalytic activity under visible-light irradiation. Compared with pure Ag₃PO₄, Bi₂WO6, Bi₂WO6/MWCNTs, and Ag₃PO₄/Bi₂WO6, ternary Ag₃PO₄/Bi₂WO6/MWCNTs nanocomposites showed the best photocatalytic performance due to the narrow band gap, large specific surface area, high charge separation efficiency, and strong light absorbance in the visible region. Degradation experiments involving norfloxacin (NOR) antibiotics under visible-light irradiation confirmed ideal photocatalytic activity of Ag₃PO₄/Bi₂WO6/MWCNTs nanocomposites. Degradation products of NOR were identified via LC-MS/MS analysis, and a potential photodegradation mechanism of NOR was discussed; results indicated that these antibiotics could be degraded via three pathways. The piperazinyl ring was the most reactive site for hydroxyl radical attacks, followed by stepwise oxidation and further ring-opening. Overall, the composites appear to be promising materials for removing contaminants from water.