This study explores how young people’s mental health was affected by the COVID-19 pandemic using artwork and semi-structured interviews. This is important to understand so that policy and practice professionals can support those affected, prepare, and respond to future crises, and support young people who are isolated and restricted in other contexts. Co-designed participatory art workshops and interviews were conducted with 16–18-year-olds (N = 21) from the London-based Longitudinal cohort Study of Cognition, Adolescents and Mobile Phones (SCAMP). Artworks and interview transcripts were qualitatively co-analysed with young people. From interviews, six themes were identified: adaptation, restriction, change, challenges, overcoming adversity, and lockdown life. From artwork, four themes were identified; trapped, negative mental wellbeing, positive emotions, and technology. Everyday factors such as home environment, relationships, hobbies, habits, and education or work were key determinants of how challenged and restricted participants felt, and their capacity to overcome this. This implies that young people’s mental health services should collaborate with other sectors to address wider life determinants in a holistic way, and that clearer guidance and support in these areas could mitigate the negative mental health impacts of major environmental changes on young people.