Influencing healthy public policy through health advocacy remains challenging. This policy analysis research uses theories of agenda setting to understand how health came to be considered for specific mention in legislation arising from land-use planning system reform in New South Wales, Australia. This qualitative study follows critical realist methodology to conduct a policy analysis of the case. We collected data from purposively sampled in-depth interviews (n ¼ 9), a focus group and documentary analysis. We used three classic policy process (agenda setting) theories to develop an analytic framework for explaining the empirical data: Multiple Streams; Punctuated Equilibrium Theory and Advocacy Coalition Framework. The reform process presented a window of opportunity that opened incrementally over a 2 year period. The opportunity was grasped by individual policy entrepreneurs who subsequently formed a coalition of healthy planning advocates focused on strategically positioning 'health' as legislative objective for the new system. The actual point of influence seemed to appear suddenly when challenges to a perceived economic development agenda within the reforms peaked, and the health objective, see as non-threatening by all stakeholders, was taken up. Our analysis demonstrates how this particular point of influence followed sustained long-term activity by health advocates prior to and during the reform process. We demonstrate a theory-driven policy analysis of health advocacy efforts to influence an instance of major land-use planning reform. The application of multiple policy process theories enables deep understanding of what is required to effectively advocate for healthy public policy.