This article focuses on the psychology of principled nonviolent activism, specifically ideas associated with Martin Luther King, Jr.’s philosophy of nonviolence and how they are compatible with attachment theory and related areas of modern neuroscience (e.g., attachment/social neuroscience and interpersonal neurobiology). The proposed Kingian Neuro-Relational Theory (KNRT) recognizes King as having a relational development approach to social justice. KNRT offers a way of understanding King’s ideas to aid research and develop strategies for reducing many forms of societal violence, with eventual outcomes of improving mental and physical health via stress reduction, and subsequent creation of a more socially just world. KNRT is an integrative, multidisciplinary approach, incorporating the philosophy of nonviolence, attachment theory, social neuroscience, ecological systems theory, and personalistic philosophy. The theory highlights developmental and clinical implications of moving beyond tactical/pragmatic nonviolent activism (nonviolent direct action) to activism via embracing nonviolence as a principled way of life (nonviolent daily interactions). This theory is building on an earlier project that conveyed how King’s philosophy of nonviolence is related to modern–day diversity and inclusion efforts.