This systematic review investigates evidence on the association between body image concerns and weight-related behaviours of adolescents and emerging adults. It includes peer-reviewed journal articles reporting research involving body image concerns and weight-related behaviours of adolescents and emerging adults, published between 2005–2017, and located through systematic searches from four databases. This review includes studies from 11 countries or regions: United States (n = 13), Asia (n = 9), Europe (n = 8), Middle East (n = 3), South America (Brazil; n = 3), Canada (n = 3), Australia (n = 1), New Zealand (n = 1), Trinidad (n = 1), Turkey (n = 1) and Seychelles (n = 1); 24 different countries (n = 1); three Asian countries and the United States (n = 1). Out of 46 studies included in this review, 45 studies reported a positive association between body image concerns and weight-related behaviours. Adolescents and emerging adults who misperceived their weight engaged in weight-related behaviours. Higher body dissatisfaction had a significant association in the development of eating disorders and extreme weight-loss behaviours. Body image concerns play a significant role in adolescents and emerging adults engaging in weight-related behaviours. Experimental research designs are required to determine the causality of this association. Evidence strongly suggests policy makers and public health practitioners contemplate strategies to promote positive body image and healthy weight-related behaviours among adolescents and emerging adults.