Both photothermal therapy (PTT) and chemodynamic therapy (CDT) are designed to focus their antitumor effect on only the tumor site, thereby minimizing unwanted severe damage to healthy tissue outside the tumor. However, each monotherapy is limited in achieving complete tumor eradication, resulting in tumor recurrence. The combination of multiple therapies may help to overcome the limitations of single therapy, improve the chances of complete tumor eradication, and reduce the risk of recurrence. Here, we report a novel multifunctional carrier-free nanoparticle, namely Mn-TPP@ICG, prepared through the self-assembly of ICG and 5,10,15,20-Tetraphenyl-21H,23H-porphine manganese (III) chloride (Mn-TPP). The prepared Mn-TPP@ICG allowed dual-mode imaging in the form of magnetic resonance imaging (MRI) and near-infrared (NIR) fluorescence imaging, as well as combination therapy in the form of CDT and PTT. In vitro experiments revealed that Mn-TPP@ICG nanoparticles can enable CDT by converting intratumoral hydrogen peroxide (H