Programs to increase emerging and established HIV and tuberculosis (TB) researchers' capacity to be more effective leaders and mentors are urgently needed in low- and middle-income countries (LMICs). Although conceptual frameworks of mentoring and mentoring toolkits have been developed by and for researchers in LMIC settings, few mentor training programs have been implemented and evaluated in these settings. We created, implemented, and evaluated a 9-month, certificate-level mentorship training program to strengthen the pipeline of HIV and TB researchers in South Africa. Differentiating features of the program included careful contextualization of mentorship tools and approaches, inclusion of a leadership curriculum to improve participant ability to work effectively in teams and organizations, and attention to processes that promote interinstitutional collaboration in mentorship. Twelve mid-career researchers graduated from the first cohort of the program. Among participants, we observed significant longitudinal improvement in mentorship competencies, increased numbers of network connections in multiple domains of collaboration, and high levels of satisfaction. We anticipate that the program description and results will be useful to researchers, research institutions, and funders seeking to build research mentorship and leadership capacity in LMIC settings.