In Australia and internationally there is a strong policy commitment to the redesign of health services toward integrated physical and mental health care. When executed well, integrated care has been demonstrated to improve the access to, clinical outcomes from, and quality of care while reducing overtreatment and duplication. Despite the demonstrated effectiveness and promise of integrated care, exactly how integrated care is best achieved remains less clear. The aim of this review study was to identify factors that support the implementation of integrated care between physical and mental health services. An integrative review was conducted following the framework developed by Whittemore and Knafl, with quantitative and qualitative evidence systematically considered. To identify studies, Medline, PubMed, PsychINFO, CINAHL were searched for the period from 2003 to 2018, and reference lists of included studies and review articles were examined. Nineteen studies were included. Synthesis of study findings identified seven key factors supporting the implementation of integrated care between physical and mental health services:(a) adequate resourcing, (b) shared values, (c) effective communication, (d) information technology (IT) infrastructure, (e) flexible administrative organizations, (f) role clarity and accountability, and (g) staff engagement and training. There was little theoretical development in included studies, with little insight into the contextual factors or underlying mechanism required to support the implementation of integrated care initiatives. This review identified a set of inter-related barriers and facilitators which, if addressed, can improve the implementation and sustainability of truly integrated care.