High-cost medicines (HCMs) can be clinically impactful for individual patients but are also subject to variable funding mechanisms. Public hospitals and health services are often asked to fund HCMs, but inconsistent processes frequently create large variations in care. CATAG (Council of Australian Therapeutic Advisory Groups) is the Australian peak national advisory body for the quality use of medicines in hospitals and health services, with all states and territories collaborating to support Drug and Therapeutics Committees (DTCs). CATAG has developed national Guiding Principles to assist DTCs to effectively govern HCMs. An established process for the development of CATAG Guiding Principles was undertaken to develop these Guiding Principles. This includes the formation of an Expert Advisory Group (EAG) comprising individuals with recognised expertise, development of draft principles and stakeholder consultation from within the CATAG membership and externally. All feedback was discussed, and changes were agreed upon. The final version was approved by the EAG and CATAG members. This document represents a summary of the seven Guiding Principles developed, covering the areas of governance, application and assessment, communication, training and resourcing. Although many outstanding priorities still exist, including the development of national coordination regarding HCM assessment, these Guiding Principles offer a basis to navigate this complex area.