Issue AddressedIntersectoral action is integral in promoting population health and health equity. In South Australia, public health partnership authorities (PHPAs) are one mechanism to promote intersectoral collaboration for addressing complex public health issues. This case study examined contemporary evidence on the critical elements of successful partnerships, explored the role of formalisation in success, and examined how identified critical elements were operationalised over time in an existing PHPA.MethodsIn the first phase, a scoping review was conducted. The second phase was a retrospective longitudinal case study of a government‐academic PHPA agreement, involving partnership document review and key informant interviews. Data triangulation and iterative thematic analysis were performed.ResultsThe critical elements of successful partnership, triangulated through multiple data sources, are mutuality, governance, communication, resources, leadership, and interactions and relationships. These elements have a high degree of interdependence. Trust supports and is reinforced by these elements, particularly during times of change or crisis. Formalisation of a partnership supports success in many ways but is insufficient on its own.ConclusionOperating in dynamic environments, a partnership requires dedicated time and effort to be successful. Attention to the strength and interconnectedness of the critical elements over the course of a partnership is crucial.So What?This case study describes how the elements of successful partnership can be applied to progress beyond transactional relationships towards authentic collaboration and overcome cross‐border and cross‐boundary public health challenges to promote population health and well‐being.