The yearning for peace within and the world around is a fundamental human aspiration. However, despite numerous philosophical and spiritual traditions grappling with its essence, a comprehensive framework for understanding and cultivating peace remains elusive. Personal peacefulness also remains a complex concept often relegated to peace explorations. This paper introduces the Capability Theory of Personal Peacefulness (CTPP), a novel framework built upon the capability approach that offers a robust foundation for understanding and fostering individual and, thereby, societal peace. CTPP offers a holistic and dynamic approach to peace that emphasises the interconnectedness of individual well-being, social harmony, and environmental sustainability. This paper explores the foundational principles of CTPP and its implications with insights into the Capability Approach and Peace Psychology. This paper argues that CTPP provides a valid and valuable peace theory worthy of further theoretical development and empirical exploration. CTPP extends beyond describing the state of peace to advocate for specific ethical standards, capabilities, and conditions that should be pursued to realise peace at personal and societal levels. It provides a framework for what peace should look like and how it can be achieved, making it a guiding theory for both personal conduct and public policy to foster a more harmonious world.