<p>Research has documented relationships between adolescent body weight and mental health, but few studies have examined profiles of adolescent weight status and weight management behaviours and mental health outcomes at population level. Utilising data from the Millenium Cohort Study (MCS), a TwoStep cluster analysis identified four clusters (i.e., underweight, no diet/ exercise; overweight, diet/exercise; normal weight, no diet / exercise; and normal weight, diet / exercise). Young women and young people who reported self-harm / suicidality and weight stigma were more likely to be in the overweight and normal weight (diet/ exercise) groups. Young people who intended to lose weight were more likely to be in the overweight (diet/exercise) and normal weight (diet/exercise) groups. Significant group differences in mental health and wellbeing outcomes at age 20, post-Covid19, were found. Young people in the overweight and normal weight (diet/ exercise) groups, and those in underweight (no diet/exercise) group self-reported significantly higher anxiety- and depression-like symptoms, psychological distress and reduced mental wellbeing than those in the normal weight (no diet/ exercise) group. Compared to young people with normal weight (no diet/exercise) those who were of normal weight and dieted and exercised reported reduced wellbeing, and anxiety and depression symptoms at age 20. Managing body weight alone may not be enough to support mental health and wellbeing in young adults, requiring a holistic approach towards reducing weight concerns and body dissatisfaction. The findings support prevention efforts to mitigate mental health difficulties in adolescents and young adults while weight concerns and stigma are taken into consideration. </p>