Theranostic agents for combined chemo-photothermal therapy have attracted intensive interest in the treatment of multi-drug resistance (MDR) in cancer therapy. However, the development of simple theranostic agents as dual hosts for both heat and a high payload of chemotherapeutic agents remains a big challenge. Herein, mesoporous polydopamine nanoparticles (MPDA) were successfully developed with properties of a high payload of DOX (up to 2000 μg mg⁻¹) and the drug efflux inhibitor TPGS (D-α-tocopheryl polyethylene glycol 1000 succinate), as well as strong near-infrared absorption. Particularly, DOX and TPGS were sequentially loaded in the pore space and on the external particle surface of MPDA via π–π stacking and hydrophobic interactions, resulting in a MPDA–DOX@TPGS complex. The DOX release observably relies on the pH value and glutathione (GSH). Furthermore, it is possible to accelerate the rate of drug release by NIR irradiation. Importantly, the MPDA–DOX@TPGS complex was found to escape from endosomes after cellular uptake and release the loaded drugs into the cytosol. By TPGS mediated MDR reversal, the delivered DOX induced significant cytotoxicity to MCF-7/ADR cells. Besides, MPDA can absorb the NIR light and convert it into fatal heat to kill the cancer cells. As a consequence, the combined therapy in our system yields a synergistic effect with high therapeutic efficacy.