BACKGROUND: Finding effective intervention strategies to combat rising obesity levels could significantly reduce the burden that obesity and associated non-communicable diseases places on both individuals and the National Health Service. METHODS: In this parallel randomised-controlled trial, 76 participants who are overweight or obese (50 female) were given free access to a fitness centre for the duration of the 12-week intervention and randomised to one of three interventions. The commercial intervention, the Healthy Weight Programme, (HWP, n = 25, 10/15 men/women) consisted of twelve 1-h nutrition coaching sessions with a nutritionist delivered as a mixture of group and 1 to 1 sessions. In addition, twice-weekly exercise sessions (24 in total) were delivered by personal trainers for 12 weeks. The NHS intervention (n = 25, 8/17 men/women) consisted of following an entirely self-managed 12-week online NHS resource. The GYM intervention (n = 26, 8/18 men/women) received no guidance or formal intervention. All participants were provided with a gym induction for safety and both the NHS and GYM participants were familiarised with ACSM physical activity guidelines by way of a hand-out. RESULTS: The overall follow-up rate was 83%. Body mass was significantly reduced at post-intervention in all groups (HWP: N = 18, – 5.17 ± 4.22 kg, NHS: N = 21-4.19 ± 5.49 kg; GYM: N = 24-1.17 ± 3.00 kg; p < 0.001) with greater reductions observed in HWP and NHS groups compared to GYM (p < 0.05). Out with body mass and BMI, there were no additional statistically significant time x intervention interaction effects. CONCLUSIONS: This is the first study to evaluate the efficacy of both a free online NHS self-help weight-loss tool and a commercial weight loss programme that provides face-to-face nutritional support and supervised exercise. The findings suggest that both interventions are superior to an active control condition with regard to eliciting short-term weight-loss. TRIAL REGISTRATION: ISRCTN Registry - ISRCTN31489026. Prospectively registered: 27/07/16.