Introduction People with multiple sclerosis (MS) are less physically active, and more sedentary than their peers despite evidence that activity helps to manage MS-related symptoms. Traditional approaches to increasing physical activity, such as exercise programmes, can be challenging for people with MS, especially those with walking disability. Focusing on decreasing prolonged sitting,and increasing light-intensity activities may be more feasible and result in more sustainable behaviour change in persons with MS. This paper describes the rationale and development of a sedentary behaviour intervention targeting persons with MS.