Background: Obesity is a risk factor for developing multiple sclerosis (MS) and MS-related disability. The efficacy of behavioral weight loss interventions among people with MS (pwMS) remains largely unknown. Objective: Examine whether a group-based telehealth weight loss intervention produces clinically significant weight loss in pwMS and obesity. Methods: Seventy-one pwMS were randomized to the weight loss intervention or treatment-as-usual (TAU). The 6-month program promoted established guidelines for calorie reduction and increased physical activity. Anthropometric measurements, mobility tasks, self-report questionnaires, and accelerometry were used to assess changes at follow-up. Results: Mean percent weight loss in the treatment group was 8.6% compared to 0.7% in the TAU group (p <.001). Sixty-five percent of participants in the intervention achieved clinically meaningful weight loss (⩾ 5%). Participants in the treatment group engaged in 46.2 minutes/week more moderate-to-vigorous physical activity than TAU participants (p =.017) and showed improvements in quality of life (p =.012). Weight loss was associated with improved mobility (p =.003) and reduced fatiguability (p =.008). Conclusion: Findings demonstrate the efficacy of a behavioral intervention for pwMS and obesity, with clinically significant weight loss for two-thirds of participants in the treatment condition. Weight loss may also lead to improved mobility and quality of life. [ABSTRACT FROM AUTHOR]