Planetary health is a transdisciplinary approach that aims to advance the understanding of the links between human-driven changes to the planet and their consequences, and to develop appropriate solutions to the challenges identified. This emerging movement has not yet agreed upon a code of ethics to underpin the rapidly expanding body of research being carried out in its name. However, a code of ethics might support the principles for planetary health set out in the Canmore Declaration of 2018. Phrases such as “Public Health 2.0”, “Human Health in an Era of Global Environmental Change”, or “A safe and just operating space for humanity” are often used in planetary health discussions, but are not always clearly defined and so far, the field lacks a strong guiding ethical framework. In this paper, we propose a starting point towards a code of ethics for planetary health that builds on the Canmore Declaration. We chose to propose 12 ethical principles in recognition of the need for a 12-Step Programme for the planet. The human race must identify and reject damaging behaviours. Evidence of the harm we are causing the planet is no longer enough and refraining from certain current practices is essential for Earth’s future health. We must motivate advocacy and calls for action. We believe a shared ethical code can act as a tool to enable and encourage that process. This paper is presented to the planetary health community as a starting point, not as a finished agenda. We welcome comments, critiques, additions and the opportunity to rework our approach accordingly.