Background: Leadership competencies are crucial for the students of medical, nursing, and other health disciplines due to their prospective roles in decision-making, teamwork, communication, and health crisis management. However, the contribution of the formal teaching sessions in health professions curricula to leadership and communication skills is inconsistent globally, including within the Palestinian undergraduate education system. To address this gap, the researchers evaluated the effectiveness and impact of the online leadership training program on the participants’ leadership competencies, aiming to identify effective adjuncts to formal curricula. Methods: This study employed a one-group pretest–post-test design. The intervention was an online training program conducted via Zoom Meetings Platform for a duration of 2 hours. The training curriculum was designed in accordance with the Medical Leadership Competency Framework (MLCF). Participants were recruited through a call for registration posted on the website of the International Medical Education Trust 2000. Pre-training/post-training impact assessment was conducted using the Medical Leadership Competence Scale (MeLeCoS). Data were analyzed using descriptive statistics and paired t-tests. Results: A total of 76 participants (65.8% undergraduates and 34.2% postgraduates) were enrolled in the study. The training significantly enhanced the participants' leadership competencies, as evidenced by the increase in the mean MeLeCoS score from 3.65 (±0.54) to 3.98 (±0.55) out of 5 (mean difference 0.33; 95% CI 0.20–0.45; p<0.001). Significant improvements were observed in five MeLeCoS factors (all p<0.001). No significant differences in the MeLeCoS scores between both sexes, study discipline, or training phase (p-values > 0.05). Conclusion: The online leadership training program markedly improved the participants' leadership competencies and emerged as a potential adjunct to formal curricula.