The prevalence of adults who are living with overweight or obesity has been increasing throughout the past three decades, which is contributing to increased healthcare costs. The Wellness Institute (WI) is a medical fitness facility that provides programs for chronic disease management. To combat the rise in overweight and obesity rates, the WI decided to create a personalized program based on a lifestyle approach with a targeted audience of individuals living with overweight or obesity. This program is known as the Weight Loss Clinic (WLC) and represents the first program targeted at individuals living with overweight or obesity with a multidisciplinary team of health professionals, such as physician oversight, Registered Dietitian, exercise specialist, and cognitive behavioural therapist or a psychologist. The thesis objective is to assess the feasibility and efficacy of a clinically-managed weight loss program. The WLC is composed of a multidisciplinary team and is based on the transtheoretical model (TTM) approach. Based on the literature review, it was found that there is insufficient evidence about the effectiveness of TTM and a multidisciplinary approach. An evaluation was conducted to further investigate the effectiveness of the clinically-managed weight loss program, specifically the WI. The program is 17-weeks long with a three-stage progression (assessment, intensive, transformation). Statistical analysis was performed using R Studio. The effects of participation were analyzed by the R generalized linear model using a pre- post- design. Other outcomes were analyzed through a paired t-test. A total of 26 participants were included in the evaluation (13 incomplete and 13 complete). The results from the evaluation indicate that participating in the weight loss program leads to significant weight loss (p=0.0009) and significant improvements in waist circumference (p=0.0002), systolic blood pressure (p=0.0052), diastolic blood pressure (p=0.0057), and body fat percentage (p=0.0001). The data generated from this evaluation will be used by the WI to improve and support the mission of the program in using an evidence-based methodology. As well, this data may be used for future clinical trials and as a model for other health institutes across the province, within Canada, and globally.