The integration of multifunctional therapeutic capabilities into a single nanosystem has attracted much attention for use as an efficient cancer therapy. However, developing biocompatible therapeutic nano-agents with desirable safety, efficiency, targeting, and synergistic effects remains challenging. Herein, we designed a class of multifunctional PEGylated magnetic nanoparticles (NPs) with a core-shell structure and polydopamine (PDA) coating, which were loaded with the anticancer drug doxorubicin (DOX) for simultaneous targeted chemotherapy and photothermal ablation of tumour cells. This nanosystem showed strong near-infrared absorption due to the polydopamine layer and was capable of magnetic field-guided drug delivery due to the superparamagnetism of the carrier. The resultant product exhibited excellent stability and biocompatibility in vitro due to the PEGylation of dopamine. Notably, the combination of chemotherapy and photothermal therapy had an evident synergistic effect on the ablation of tumour cells. This multifunctional nanoplatform has promising potential as an efficient therapeutic agent for multimodal cancer treatment.