This study examined the long-term and mediation effects of a need-supportive coaching programme on physical activity. Sedentary employees (n = 92) of the university of Leuven received 4 months of physical activity coaching, based on the self-determination theory, by coaches with a bachelor's degree in kinesiology who are specializing in health-related physical activity (n = 30). The programme consisted of a limited number of individual contact moments (i.e. an intake session, three follow-up contacts and an out-take session), either face-to-face, by phone or by e-mail. Self-reported physical activity, social support, self-efficacy and autonomous motivation were assessed in the coaching group (n = 92) and a control group (n = 34) at three moments: before the intervention (i.e. pre-test), after the intervention (i.e. post-test) and 1 year after pre-test measurements (i.e. follow-up test). Results revealed significant 3 (time) × 2 (groups) interaction effects on strenuous and total physical activity. Moreover, whereas the control group remained stable from pre- to post-test, the coaching group increased significantly in moderate, strenuous and total physical activity. Additionally, the coaching group increased significantly in mild, moderate, strenuous and total physical activity from pre- to follow-up tests, whereas the control group did not change. Bootstrapping analyses indicated that self-efficacy and autonomous motivation significantly mediated the intervention effect on physical activity from pre- to post-test, while social support significantly mediated the long-term effect. This study provides evidence for the long-term effectiveness of a need-supportive physical activity programme that might be efficient at the community level.