This study took place at SUNY Buffalo State College in Buffalo, NY during the 2018-2019 academic year, and was conducted to examine the effect of the Health Ambassador (HA) program on reducing drinking, drug use, and other potential detrimental health behaviors among Greeks and athletes. Study participants included 147 participants derived from two groups of undergraduate students. Group 1 included 18 students who participated in the Health Ambassador program. Group 2 included 129 men and women who were recruited from three athletic teams and two campus sororities. Group 2 was further divided into intervention and control groups. A five-week multi-phase health and leadership intervention, consisting of health and leadership trainings and workshops, was implemented over two semesters. Through a blended approach, which incorporated both in-person and online trainings, health ambassadors were educated in health and leadership content and developed prevention workshops to positively influence Greeks and athletes' perceptions and behaviors toward substance use. Following the trainings, the health ambassadors delivered these substance prevention workshops to members of the intervention group. Self-Efficacy Theory and the Theory of Planned Behavior served as the theoretical frameworks for this study in order to determine health ambassador opinions around serving as student leaders and assess Greek and athletic student beliefs over engaging in potentially unsafe health behaviors, including alcohol and substance abuse. The study employed a convergent parallel mixed methods approach where both quantitative and qualitative data were collected concurrently, analyzed separately, and compared to determine if the results substantiated each other. Taken from surveys, questionnaires, group interviews, observations, and field notes, this study shows that (1) past 30 day use of alcohol, binge drinking, and marijuana positively decreased following the health ambassador intervention, (2) intervention group participants became more effective at refusing drugs and alcohol and were more confident in making healthier choices, (3) health ambassadors overcame initial fears and biases toward working with Greeks and athletes, and achieved success presenting health material and functioning as student leaders, (4) the individual and collective efficacy of the health ambassadors positively increased. Additionally, study limitations, implications for research, implications for practice, and conclusions were discussed.