Abstract Aim To analyse the relationships between mental health and employment commitment among prisoners and the long-term unemployed (LTU) trying to return to work. Method Fifty-two of 62 male inmates of a semi-open prison (Givenich Penitentiary Centre, the only such unit in Luxembourg), and 69 LTU registered at the Luxembourg Employment Administration completed a questionnaire exploring: 1) mental health (measured by means of scales GHQ12 and CES-D); 2) employment commitment; 3) availability of a support network, self-esteem, empowerment; and 4) socio-demographic characteristics. Results Compared with LTU, inmates were younger, more had work experience (54.9% vs 26.1%), and more were educated to only a low level (71.1% vs 58.0%). The link between employment commitment and mental health in the LTU was the opposite of that seen among the prisoners: the more significant the perceived importance of employment, the worse the mental health (GHQ12 p = 0.003; CES-D p < 0.001) of the LTU; in contrast, among prisoners, the GHQ12 showed that the greater the perceived value of work, the lower the psychic distress (p = 0.012). Greater empowerment was associated with less depression in both populations. The education levels of people who did not reach the end of secondary school, whether inmates or LTU, were negatively linked with their mental equilibrium. Conclusion The two groups clearly need professional support. Future research should further investigate the link between different forms of professional help and mental health. Randomized controlled trials could be carried out in both groups, with interventions to improve work commitment for prisoners and to help with getting a job for LTU. For those LTU who value employment but cannot find it, the best help may be psychological support.