The majority of the world’s total prison population resides in low- and middle-income countries (LMIC), but most research into the prevalence of mental illness and suicide risk comes from high-income countries (HIC). The provision of mental health care varies widely across prisons in LMIC, with reported disparity between high levels of need and funding, resources and services. This rapid review aims to explore the existing evidence-base relating to suicide and mental health prevalence in prisons in LMIC. A total of 2,799 published and grey literature were identified through systematic searches, with 35 papers included in the final review. The prevalence of suicide ideation was lower among prisoners in LMIC than HIC, with common mental illness, severe mental illness, and substance misuse more prevalent among LMIC prisoners. Rates of suicide ideation and common mental illness were higher among females than males. These findings highlight the need for dedicated research using LMIC samples and consideration of resources within LMIC prisons. The results of this analysis can be used to inform next steps to tackle the high level of unmet mental health needs amongst prisoner populations in LMIC.