Aim The current study aims to qualitatively identify determinants, barriers and facilitators of physical activity among a population with mental health disorders. Subject and methods Seventeen participants with moderate mental disorders were recruited. Semi-structured interviews were conducted to identify physical activity facilitators and barriers. Data were organized and analysed in ATLAS.ti, mainly based on a generic qualitative research approach. Results Most participants found physical activity important and expressed a positive attitude towards it. In general, higher self-efficacy and more social support were beneficial for participants’ physical activity levels. Reasons/facilitating factors to be more physically active were: having fun, good weather, progress, routine, self-compassion and a stimulating environment. Barriers were not having fun, being busy, mental complaints, lack of energy, procrastination and physical complaints. Conclusion Future interventions could promote physical activity among people with moderate mental disorders to help them identify and overcome barriers. The newly identified determinant ‘self-compassion’ could be an interesting target for promoting physical activity in this group of people with moderate mental disorders.