Background: Mentorship is critical to success in postgraduate science, technology, engineering, math, and medicine (STEMM) settings. As such, the purpose of this study is to comprehensively explore the state of mentorship interventions in postgraduate STEMM settings to identify novel practices and future research directions. The selection criteria for reviewed articles included: (1) published between 2002 and 2022, (2) peer-reviewed, (3) in English, (4) postgraduate mentees, (5) a program where mentorship is a significant, explicit focus, and (6) a description of mentee outcomes related to the mentorship intervention. Overall, 2583 articles were screened, and 109 articles were reviewed. Results: Most postgraduate STEMM mentorship intervention studies lack strong evidence to evaluate the effectiveness of the intervention, with only 5.5% of articles designed as randomized controlled trials. Most mentorship interventions (45.6%) were created for faculty, and few (4%) were for postdoctoral researchers. Also, only 18.8% of interventions focused on underrepresented groups in STEMM. Most interventions (53.7%) prescribed a dyadic structure, and there was more mentorship training for mentors than mentees. Conclusion: Overall, these findings identify gaps in mentorship interventions and provide step-by-step guidance for future interventions, including a consideration for underrepresented groups and postdoctoral scholars, robust mentorship training, and more randomized controlled trials.