Obesity rates are on the rise worldwide. Nearly 1 in every 4 Canadians is classified as being overweight. With an increase in obesity, there is also a correlated rise in its comorbidities, most notably Type-2 Diabetes Mellitus (T2DM). Bariatric surgery is superior to diet and lifestyle management in managing the severe obese. These bariatric procedures are traditionally classified as either being restrictive(reducing caloric intake), or malabsorptive (re-routing the gastrointestinal tract). The roux-en-Y gastric bypass (RYGB) is the most commonly performed bariatric surgery. Studies have shown that post-RYGB, there is a significant improvement or even complete resolution in patients' type-2 diabetes mellitus (T2DM), with significantly more patients achieving euglycemia compared to the control population. RYGB has also been shown to prevent the development of T2DM. When RYGB was compared to more restrictive procedures, it achieved superior results in both weight-loss and T2DM resolution and the maintenance of these results long-term. The superiority of procedures, such as RYGB, is potentially explained through alterations in gut hormones, ghrelin and GLP-1. In this review, we explore the role of bariatric surgery in the prevention and treatment of T2DM, with a specific focus on the recent evidence surrounding surgical treatment via RYGB.