Background: The global COVID-19 pandemic has escalated the prevalence of mental illness in the community. While specialist mental health nurses have advanced training and skills in mental health care, supporting mental health is a key role for all nurses. As front-line health care professionals, primary health care (PHC) nurses need to be prepared and confident in managing mental health issues. Aim: To critically analyse and synthesise international literature about the knowledge gaps and learning needs of PHC nurses in providing mental health care. Design and methods: An integrative review. The quality of papers was assessed using the Mixed Methods Appraisal Tool. Data were extracted into a summary table and analysed using narrative analysis. Data sources: CINAHL, Ovid MEDLINE, Web of Science and EBSCO electronic databases were searched between 1999 and 2019. Papers were included if they reported original research which explored mental health education/training of nurses working in PHC. Findings: Of the 652 papers identified, 13 met the inclusion criteria. Four themes were identified: preparedness; addressing knowledge gaps, education programs, and facilitators and barriers. Discussion: Despite increasing integration of physical and mental health management in PHC, there is limited evidence relating to knowledge gaps and skills development of PHC nurses or their preparedness to provide mental health care. Conclusion: Findings from this review, together with the global increase in mental illness in communities arising from COVID-19, highlight the need for PHC nurses to identify their mental health learning needs and engage in education to prepare them to meet rising service demands.