Multifunctional intelligent theranostics agents are promising for next-generation oncotherapy. We fabricated a tumor-microenvironment (TME)-responsive carbon nanotube (CNT)-based nanoplatform for T1 weighted magnetic resonance imaging (MRI)-guided synergistic photodynamic and photothermal therapy (PDT and PTT). CNTs convert near infrared (NIR) radiation into hyperthermia for PTT, and can effectively deliver their cargo into cells due to their unique 1D nanostructure. The CNT@MnO2-PEG@Ce6 nanomedicine was internalized into tumor cells, and rapidly released the photosensitizer (Ce6) in response to the low pH and high glutathione (GSH) levels characteristic of the TME. The degradation of the MnO2 layer under the same conditions released Mn2+ for T1-MRI. Furthermore, catalytic decomposition of the excess H2O2 into oxygen by MnO2 enhanced the efficacy of PDT, relieved hypoxia, and increased consumption of superfluous GSH to mitigate the effects of excessive reactive oxygen species (ROS) generation during PDT. MRI-guided PDT and PTT synergistically inhibited tumor cell growth in vitro, and ablated tumors in vivo. The side effects were negligible due to specific tumor cell targeting via surface modification with folic-PEG, and enhanced permeability and retention. Taken together, CNT@MnO2-PEG is a fully TME-responsive theranostics nanoplatform for targeted tumor ablation and real-time disease tracking.