This study examines the efficacy of mindfulness-based training programmes in cultivating sustainability mindsets among business leaders. Through qualitative analysis of 20 executive participants in a business school master's programme, the research investigates how mindfulness practices facilitate sustainable leadership development across three dimensions: knowing, being, and doing. The investigation employs longitudinal methodological approaches, incorporating pre-intervention document analysis and semi-structured interviews to examine participants' experiential learning. Findings reveal that mindfulness training catalyses sustainable mindset development through twelve distinct mechanisms, equally distributed across cognitive, existential, and practical domains. These mechanisms operate at personal, relational, and institutional levels, enhancing leaders' capacity to address complex sustainability challenges. Results demonstrate that mindfulness practices fundamentally transform leadership approaches by fostering enhanced interoceptive awareness, strengthened interpersonal dynamics, and expanded institutional consciousness. The study contributes to existing literature by establishing empirical links between mindfulness practices and sustainability mindset development, whilst providing practical insights for business schools seeking to integrate experiential learning approaches into leadership development programmes.