BackgroundIn most developed nations, there has been a shift from public services to a marketisation of public goods and services - representing a significant reform process aiming to transform the way in which community-based human services, such as health, are delivered and consumed. For services, this means developing the capacity to adapt and innovate in response to changing circumstances to achieve quality. The availability of rigorous research to demonstrate whether a market approach and contestability, in particular, is a coherent reform process is largely absent. Contestability operates on the premise that better procurement processes allow more providers to enter the market and compete for contracts. This is expected to create stimulus for greater efficiencies, innovation and improved service delivery to consumers. There is limited understanding, however, about how community-based providers morph and re-configure in response to the opportunities posed by contestability. This study focuses on the effect of a contestability policy on the community-managed mental health sector.Methods/designA realist review will be undertaken to understand how and why the introduction of contestability into a previously incontestable market influences the ways in which community-based mental health providers respond to contestability. The review will investigate those circumstances that shape organisational response and generate outcomes through activating mechanisms. An early scoping has helped to formulate the initial program theory. A realist synthesis will be undertaken to identify relevant journal articles and grey literature. Data will be extracted in relation to the emerging contextual factors, mechanisms and outcomes and their configurations. The analysis will seek patterns and regularities in these configurations across the extracted data and will focus on addressing our theory-based questions.DiscussionIncreasingly, community-based mental health markets are moving to contestability models. Rigorous research is needed to understand how such markets work and in what contexts. The knowledge gained from this study in community-based mental health will provide valuable lessons in how contestability works, in what circumstances and who benefits when. The results of the proposed research will be useful to policy-makers and may be applicable in other contexts beyond the community-based mental health sector.Systematic review registrationPROSPERO CRD42015016808