The underlying tenet of evidence-based decision-making in health services is assessing all the relevant evidence. Using the traditional qualitative and quantitative approaches to identifying evidence may not capture the full spectrum of factors that need to be addressed. A selective mixed-method approach may provide a comprehensive assessment of the relevant knowledge. This paper adds to the methodological literature by outlining a novel sequential, mixed-method, exploratory process for identifying evidence-based data standards that may be used for health service decision-making. The three-phase process, entitled Delphi Plus, engages peer-nominated topic-specific experts to assess all publicly available and practice-based items and, through a series of reviews, reach an evidence-based consensus on standards for decision-making. Each process phase is outlined in-depth and supplemented by practical learnings gained through its implementation. The Delphi Plus methodology provides the first comprehensive process for combining the published and practised data to develop evidence-based data standards. The routine use of Delphi Plus would provide a framework for benchmarking in health services, enabling greater monitoring and evaluation of client outcomes and improving quality care. This manuscript describes the process of implementing Delphi Plus and provides an example of data standards generated from its use, which directly inform the Australian Government's Primary Health Care 10 Year Plan.