This study aimed to understand the effectiveness of the Mental Health First Aid (MHFA) training on improving mental health outcomes: mental health knowledge, stigma, and helping behaviours. Results from 18 trials were assessed on their effects at post-training, 6 months following training and over 6 months following training. The findings showed that there were small to moderate effects at post training and 6 months following training, however the effects at 12 months following training were less clear. Specifically, MHFA training improved mental health knowledge and recognition of a mental condition and slightly reduced levels of stigma. Other outcomes such as confidence in helping someone with mental ill-health and intentions to provide first aid were also improved. Small improvements were also noted with the amount of help provided to a person with mental ill-health, although, the quality of helping behaviours given was unclear.