Exercise is an effective intervention for improving function, mobility and health-related quality of life in people with multiple sclerosis (PwMS). Questions remain however, regarding the effectiveness of pragmatic exercise interventions for evoking tangible and sustained increases in physical activity and long-term impact on important health outcomes in PwMS. Furthermore, dose-response relationships between exercise and health outcomes have not previously been reported in PwMS. These issues, and improved knowledge of cost effectiveness, are likely to influence key decisions of health policy makers regarding the implementation of exercise therapy as part of the patient care pathway for PwMS. Hence, the primary aim of this study is to investigate whether a 12-week tapered programme of supervised exercise, incorporating cognitive-behavioural techniques to facilitate sustained behaviour change, is effective for evoking improvements in physical activity and key health outcomes in PwMS over 9 months of follow-up. A total of 120 PwMS will be randomised (1:1) to either a 12-week pragmatic exercise therapy intervention or usual care control group. Participants will be included on the basis of a clinical diagnosis of MS, with an expanded disability status score (EDSS) between 1 and 6.5. Outcome measures, to be assessed before and after the intervention and 6 months later, will include physical activity, clinical and functional measures and health-related quality of life. In addition, the cost effectiveness of the intervention will be evaluated and dose-response relationships between physical activity and the primary/secondary outcomes in those with mild and more severe disease will be explored.