Chemical warfare agents pose serious risks to human health due to their neurotoxic, immunosuppressive, and oxidative effects, while conventional antidotes remain limited by toxicity, cost, and accessibility. This review highlights phytochemicals as promising natural and sustainable countermeasures against CWA-induced toxicity. It summarizes the protective roles of flavonoids, polyphenols, terpenoids, and alkaloids in enhancing antioxidant defenses, modulating immune responses, chelating toxic metals, and mitigating neuroinflammation and organ damage. The review also discusses recent advances in nanophytochemistry that improve bioavailability and targeted delivery, as well as innovative applications in protective materials and nutraceuticals. Overall, phytochemical-based strategies offer an eco-friendly, biocompatible, and globally accessible approach to chemical warfare defense.