INTRODUCTION: Although compassionate care is an essential component of mental health nursing, understandings of the impact of compassion fatigue is poorly understood. AIMS/QUESTIONS: To examine and synthesise available data on the prevalence of compassion fatigue within mental health nurses and consider what variables impact compassion fatigue. METHOD: A search of Medline, Embase, PsychINFO, Emcare, Web of Science, Scopus, CINAHL and grey literature for articles published between 1992 and February 2021 was conducted. Data were extracted from articles meeting inclusion criteria and integrated using narrative synthesis. RESULTS: Twelve articles were included. Prevalence of compassion fatigue ranged from low to high. Variables were identified that may mitigate the risk of compassion fatigue. Strong leadership and positive workplace cultures, clinical supervision, reflection, self-care, and personal well-being may protect mental health nurses against compassion fatigue. DISCUSSION: Future research is needed on mental health nurses lived experience of compassion fatigue and their understandings of compassion. IMPLICATIONS FOR PRACTICE: Interventions should focus on increasing awareness of compassion fatigue and building individual and organisational resilience. Both organisations and individuals should be aware of the role they play in maintaining the capacity and capability for mental health nurses to provide sustainable and compassionate mental healthcare.