Leadership is a key process to achieve sustainable development, as it influences how individuals and organizations respond to complex sustainability (grand) challenges. Although Sustainability Leadership has been developed through various frameworks, many remain either theoretical or siloed, and few have been practically validated. This highlighted the need for a Holistic Sustainability Leadership (HSL) framework that connects the inner aspect of the self from Holistic Leadership with the systems thinking and long-term stewardship of Sustainability Leadership, that is practically validated. To explore and develop this, we applied an abductive research approach going from theory to data and back from data to theory. Six semi-structured interviews were conducted with experts in the fields of leadership and sustainability to validate and further refine the framework. The final version of the HSL framework consists of four interconnected aspects: Being, Doing, Developing, and Visioning that show leadership as a process that evolves between the leader and the follower / community. The framework contributes both theoretically and practically by offering a model that supports leadership development, decision-making, and long-term holistic sustainability transformation in complex environments.