Seeking achievement of health equity has underpinned national government and global health policies for decades. However, major difficulties and challenges faced in the practice of achieving “Health for All” has lead to a recognition of the need to broaden the focus of efforts to improve health equity. Civil society groups have been identified as key stakeholders in attempts to achieve health equity, and the importance of strengthening their capacity to influence relevant government policy and practice has been highlighted. This paper presents the results of a qualitative study which examined the role of organisations outside government in advocating for health equity, and the capacities and conditions which were related to their success. In-depth, unstructured interviews were conducted with 26 non-government organisations (NGOs) who were active in three important health policy debates in Australia. The grounded theory method was used to direct data collection and analysis, and member checking was employed to ensure soundness and build ownership of the findings. Effective advocacy was found to be a dynamic process characterised by flexibility and opportunism within a framework of longer term goals. Two key ways of working were identified - in partnership and in conflict with government with shifts in emphasis in response to organisational strengths and a changing environment. A number of domains of capacity which together are termed “capacity for advocacy” were also identified. It is clear that NGOs can learn a great deal from each other, but there needs to be investments by governments, international agencies and NGOs themselves if advocacy for health equity is to be strengthened.