In the absence of a single comprehensive systematic review of Rational Emotive Behaviour Therapy interventions across all settings, we reviewed the methodological quality, effectiveness and efficacy of Rational Emotive Behaviour Therapy interventions on irrational/rational beliefs. We explored the impact of Rational Emotive Behaviour Therapy on wider outcomes (e.g., mental health) and identified the characteristics of successful interventions. PsycARTICLES, PsycINFO, Scopus, SPORTDiscus, and PubMed were systematically searched up to December 2023 with 162 Rational Emotive Behaviour Therapy intervention studies identified which included a validated measure of irrational/rational beliefs. Where possible, effect size for irrational/rational belief change was reported and data was analysed through a qualitative approach. Using the Mixed Methods Appraisal tool, methodological quality within the Sport and Exercise domain was assessed as good, whilst all other domains were considered low in quality, with insufficient detail provided on intervention characteristics and delivery. Most studies were conducted in the United States, within the Education domain, and assessed irrational beliefs in non-clinical adult samples. Overall, studies reported significant reductions in irrational beliefs, increases in rational beliefs and improvements in mental health outcomes (e.g., depression). More successful interventions were delivered by trained Rational Emotive Behaviour Therapy practitioners, adopted the ABC framework and were longer in duration. We highlight the importance of designing and conducting rigorous future Rational Emotive Behaviour Therapy research to generate clearer insights as to its impact on irrational/rational beliefs and mental health outcomes.