Mental Health First Aid (MHFA) is an early intervention training course designed to improve the knowledge, skills and confidence of non-clinicians to manage mental health emergencies. The course aims to minimise the negative impact of mental distress by encouraging the early provision of appropriate care. The course has been evaluated in Australia, but less rigorously in other countries where it is offered. Previous research suggests that participants gain knowledge and skills from completing the course, however, the mechanism by which this learning occurs and the impact of completing the course on the participants' own mental well-being has not been systematically evaluated. This study evaluated the responses of 216 Irish course participants and a matched control group before and following training. Knowledge of mental ill-health, participant confidence, competence and skills to manage a mental health emergency were rated. MHFA participants' sense of mastery and mental well-being were also assessed using Pearlin and Schooler's Mastery Scale (1978), the Mental Health Index and Psychological Distress scales of the SF-36 (Ware, Kosinsk, Keller, 1996) and the Warwick Edinburgh Mental Well-being Scale (Tennant et al., 2007). MHFA course participants were assessed at two and six months following training to evaluate the robustness of their learning and the application of the learning. Findings from repeated measures analysis indicated that knowledge of mental ill-health is enhanced by MHFA training. Following MHFA training there is a statistically significant increase course the participants¿ rating of skills, confidence and competence to manage mental health emergencies, in comparison to the control group. Following training, participants reported; an enhanced sense of mastery, applying their knowledge and an increasing preparedness to offer assistance. Further, there were positive benefits for participants' mental health, with ratings of their mental well-being continuing to increase up to six months following training. MHFA training provides course participants with the knowledge and skills to assist others in distress as well as having an enduring positive impact on the participants' mental well-being. Despite this, questions still remain about the effectiveness of MHFA for those who receive care. The durability of the positive effects of the learning requires further exploration.