Can the United States legal system extend personhood to non-human entities, rivers, ecosystems, and megafauna, as a mechanism for environmental protection? This thesis investigates this question through a multidisciplinary analysis of international legal precedents, global climate litigation, and Supreme Court jurisprudence, by employing comparative case study analysis, doctrinal review, and academic literature synthesis across three methodological phases. Three primary case studies, New Zealand's Te Awa Tupua Act (2017), Australia's Victorian Environmental Water Holder (2010), and Bolivia's Law of the Rights of Mother Earth (2008), demonstrate that legal personhood for nature is institutionally viable, culturally grounded, and administratively functional when paired with guardianship structures and co-governance frameworks. A survey of six global climate litigation cases further reveals an emerging international consensus around judicially enforceable ecological obligation. By contrast, SCOTUS jurisprudence has consistently subordinated environmental protection to property rights, statutory textualism, and administrative deference. However, doctrinal openings remain within stare decisis, the Winters Doctrine, and due process frameworks. This thesis concludes that there is precedent and potential for three categories of entities—large mammals, rivers and watersheds, and named natural features—for legal personhood within the United States. This may be achieved through tribal legal systems, state constitutional amendments, federal statutory reform, and mandatory guardianship-based standing. Indigenous knowledge systems, particularly Māori and Andean cosmologies, provide not merely cultural context but active jurisprudential models for legal pluralism. The United States already possesses the legal architecture necessary for this transformation. What remains is the political and institutional will to use it.