Growing research evidence on young people’s mental health and wellbeing during Covid-19 has highlighted the importance of examining the social relationships and circumstances that surround adolescent life. This study analysed secondary data obtained from the first wave of the COVID-19 Social Mobility and Opportunities (COSMO) Study, which examined the mental health and wellbeing of young people. Through a series of multiple linear and binary logistic regression analyses, psychological distress, elevated symptoms of depression and generalised anxiety, and self-esteem and life satisfaction were examined in relation to physical health, social support, interpersonal violence (i.e., face to face bullying, cyberbullying, discrimination), and demographic background in 16-year-olds during the pandemic. The findings showed that young people were more likely to report higher psychological distress and elevated symptoms of depression and anxiety if they were female, had poor physical health and limited family and community support, and experienced bullying, cyberbullying, and discrimination. The same measures were also found to predict low self-esteem and life satisfaction. The findings have significant implications regarding the nature of mental health and wellbeing in young people and the importance of accounting for interpersonal violence and social support when examining mental health in 16-year-olds, especially during health crises. A multisectoral approach involving health and education sectors, in collaboration with family and community support services, is advocated to reduce interpersonal violence and support young people’s mental health.