Evidence on the effectiveness of workplace mental health promotion for people with disabilities is limited. This study aimed to evaluate the effectiveness of a brief mental health promotion intervention in social enterprises. It had a non-blinded cluster randomized controlled trial design with follow-up one and four months after the intervention. In total 196 employees agreed to participate (86 intervention and 110 control). Empowerment was the main outcome; secondary outcomes were resilience, palliative behavior, determinants of four coping strategies of mental health, quality of life, and life satisfaction. A brief participant satisfaction survey was conducted after the intervention. No significant intervention effect on empowerment was found. However, at one month follow-up, significant favorable effects were found on perceived social support for coping strategies for mental health and on palliative behavior. At four months follow-up, favorable intervention effects were found on quality of life, but unfavorable effects were found on unjustified worrying. In addition, the intervention was well received by the employees. This brief intervention might be a promising first step to improve mental health in people with disabilities working in social enterprises. Nevertheless, additional monitoring by professionals and managers working in the organizations might be needed to maintain these effects.