Gatekeeper training (GKT) is a common intervention aiming to prevent suicidal behavior. We investigated updated evidence for the effectiveness of GKT in suicide prevention using data from randomized controlled trials (RCTs) and intervention studies, and we also describe variations in existing GKT programs. We performed a systematic review. The literature search was conducted using PubMed, PsycINFO, CINAHL, the Cochrane databases, and reference lists from previous reviews. RCTs or intervention studies utilizing prospective or quasi-experimental designs were included. The search terms identified 343 articles. Ten randomized clinical trials and six intervention studies were identified as eligible for inclusion. Among the eligible studies, a number of different types of GKT were identified, including Question, Persuade, and Refer, Applied Suicide Intervention Skills Training, OSPI, Youth Aware of Mental Health, and approaches based on e-learning. For the RCTs, the effects of GKT remained unclear in relation to knowledge, appraisals, and self-efficacy after training, though some supportive evidence was found in the uncontrolled pre-post studies. The overall quality for each RCT was rated as either low or unclear. We could not perform a meta-analysis because comparable outcomes could not be identified across studies. The effects of GKT remain unclear. There are many variations in GKT and there is a need to replicate studies in target populations. Future research should examine the effectiveness of a standardized GKT program using high-quality RCTs which include the evaluation of pre-specified primary outcomes in comparison with appropriate control groups.