Background: We propose a Phase III trial that compares the effectiveness of an exercise training program delivered in a facility-based setting with direct, in-person supervision or a home-based setting with remote supervision via telerehabilitation for improving walking performance in persons with multiple sclerosis(MS)who have walking dysfunction and mobility disability. Methods/design: The study was developed with stakeholder engagement and is a multi-site trial that follows a 2-stage, randomized choice design. The trial compares the effectiveness of a 16-week evidence-based, individualized exercise program delivered in a supervised, facility-based setting versus a remotely coached/guided, home-based setting using telerehabilitation in physically inactive and cognitively intact people with MS who have walking dysfunction and mobility disability(N = 500). The primary outcome is walking speed. The secondary outcomes are walking endurance, disability status, and patient-reported outcomes of physical activity, walking impairment, fatigue, and quality of life. The components of the exercise program itself are similar between the groups and follow the Guidelines for Exercise in MS protocol. This includes a program manual, exercise prescription, exercise equipment, social-cognitive theory materials including newsletters, logs, and calendars, and one-on-one behavioral coaching by exercise specialists with background in MS. The main difference between groups is the coaching approach and setting for delivering the exercise training program. The outcomes will be collected by treatment-blinded assessors at baseline(week 0), mid-intervention(week 8), post-intervention(week 16), and follow-up(week 52). Discussion: The proposed study will provide evidence for the effectiveness of a novel, widely-scalable program for delivering exercise training in persons with MS who have walking dysfunction and mobility disability.