Present-day theranostic agents for tumor magnetic resonance imaging (MRI) and photothermal therapy are generally metal-based with attendant metal-specific downsides. We, therefore, designed a tumor-targeted all-organic nanotheranostic platform by effectively compartmentalizing organic nitroxide radicals in polymeric nanoparticles via amide-bond linkages. The nanoplatform features prolonged nitroxide-systemic circulation times, appreciable water dispersibility, high nitroxide loading and in vivo reduction resistance, superlative biocompatibility, and ultimate magnetic resonance-imaging sensitivity. Moreover, the metal-free folate-targeted nanoplatform conveys a plethora of polypyrrole to tumor sites for effectual MRI-guided tumor-targeted photothermal therapy. It is therefore envisaged that leveraging this study's underlying benefits will help guide the design of future all-organic-based nanoparticles in furtherance to safer tumor theranostics.