Healthcare makes a significant contribution to the social, economic and environmental benefits of communities. It is correspondingly a significant employer and consumer of both energy and consumables, often at high costs. Lean, a quality improvement methodology focuses on the elimination of non-value add (NVA) activities (steps that do not add value from the perspective of the customer) to improve the flow of people, information or goods. Increasingly, Lean thinking is evolving from its initial focus on eliminating NVA to a more holistic approach that encompasses sustainability. However, little work has been undertaken intentionally, including environmental sustainability outcomes in Lean healthcare interventions. Realist review methodology facilitates an understanding of the extent to which an intervention works, for whom, in what context, why and how, and has proven useful in research relating to Lean interventions in healthcare settings. This protocol provides details for a realist review that will enable an understanding of the specific contexts in which certain mechanisms are activated that enable the inclusion of environmental sustainability outcomes in the design of Lean healthcare improvement interventions.