Stimuli-responsive nanotherapy (SRN) has emerged as a promising therapeutic strategy that employs nanosensitizers activated by external physical or chemical stimuli to generate reactive species for disease treatment. Among various nanosensitizers, metal nanoparticles (MNPs) have attracted considerable attention owing to their unique physicochemical properties, including tunable optical responses, catalytic activity, magnetic behavior, and high surface reactivity. These characteristics enable the construction of versatile nanoplatforms for multiple dynamic therapeutic modalities. In this review, we summarize the fundamental physicochemical properties of representative metal nanoparticles and their relevance to stimulus-responsive nanotherapies. We systematically review major therapeutic modalities, including photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), piezocatalytic therapy (PCT), magnetic hyperthermia therapy (MHT), chemodynamic therapy (CDT), and electrodynamic therapy (EDT), with emphasis on their underlying mechanisms, material design, and recent biomedical applications. We further discuss the advantages and limitations of these therapeutic strategies and highlight recent advances in multifunctional nanoplatforms that integrate multiple therapeutic mechanisms to achieve synergistic effects. The biomedical applications of these metal nanoparticle-based therapies in tumor treatment, infection control, neurological disorders, bone tissue regeneration, and cardiovascular diseases are highlighted. Finally, current challenges and future perspectives are addressed, with particular emphasis on biosafety, therapeutic efficiency, stimulus control, multimodal integration, and clinical translation. This review provides an integrated overview of metal nanoparticle-based stimuli-responsive nanotherapies and highlights opportunities for the rational design of multifunctional therapeutic platforms.