Objective: People living with severe and persistent mental illness experience poorer physical health, often due to medication and preventable lifestyle factors, and exacerbated by barriers to accessing healthcare services. Pharmacists are well-positioned to improve the physical and mental health of this population. However, little is known about pharmacists’ current practices when providing services to this population nor the impact of pharmacist-led interventions on consumer health outcomes. We undertook a systematic review to identify, describe and assess the effectiveness of pharmacist-led interventions for supporting people living with severe and persistent mental illness and the impact on consumer outcomes. Methods: MEDLINE, Embase, PsycINFO, CINAHL, Web of Science, Scopus, Cochrane Library, International Pharmaceutical Abstracts and ProQuest Dissertations and Theses were searched between January 1990 and April 2020. Full-text studies exploring pharmacist-led interventions in any setting for people living with severe and persistent mental illness were included. A risk of bias assessment was conducted. Results: A total of 37 studies were included. More than half of the pharmacist interventions were multifaceted. The most common components of pharmacist-led interventions included education and/or patient counselling, providing recommendations to healthcare professionals and conducting medication reviews. Multifaceted interventions demonstrated improvements in clinical outcomes, whereas single interventions focused mostly on consumer-reported outcomes. The methodological quality of included studies was moderate-to-high risk of bias and there was considerable heterogeneity in the study design, interventions described, and outcomes reported. Conclusion: There is evidence that pharmacist-led interventions improve consumer-reported and clinical outcomes for people living with severe and persistent mental illness. Pharmacists are capable and have a role in supporting people living with severe and persistent mental illness, either individually or as interprofessional collaborators with other healthcare professionals. Future research should attempt to better understand which particular intervention components have the greatest impact and also evaluate the implementation and long-term sustainability of such interventions.