AbstractObjectiveThe disruption caused by the COVID‐19 pandemic has been associated with poor mental health, including increases in eating disorders and self‐harm symptoms. We investigated risk and protective factors for the new onset of these symptoms during the pandemic.MethodData were from the COVID‐19 Psychiatry and Neurological Genetics study and the Repeated Assessment of Mental health in Pandemics Study (n = 36,715). Exposures were socio‐demographic characteristics, lifetime psychiatric disorder, and COVID‐related variables, including SARS‐CoV‐2 infection/illness with COVID‐19. We identified four subsamples of participants without pre‐pandemic experience of our outcomes: binge eating (n = 24,211), low weight (n = 24,364), suicidal and/or self‐harm ideation (n = 18,040), and self‐harm (n = 29,948). Participants reported on our outcomes at frequent intervals (fortnightly to monthly). We fitted multiple logistic regression models to identify factors associated with the new onset of our outcomes.ResultsWithin each subsample, new onset was reported by: 21% for binge eating, 10.8% for low weight, 23.5% for suicidal and/or self‐harm ideation, and 3.5% for self‐harm. Shared risk factors included having a lifetime psychiatric disorder, not being in paid employment, higher pandemic worry scores, and being racially minoritized. Conversely, infection with SARS‐CoV‐2/illness with COVID‐19 was linked to lower odds of binge eating, low weight, and suicidal and/or self‐harm ideation.DiscussionOverall, we detected shared risk factors that may drive the comorbidity between eating disorders and self‐harm. Subgroups of individuals with these risk factors may require more frequent monitoring during future pandemics.Public SignificanceIn a sample of 35,000 UK residents, people who had a psychiatric disorder, identified as being part of a racially minoritized group, were not in paid employment, or were more worried about the pandemic were more likely to experience binge eating, low weight, suicidal and/or self‐harm ideation, and self‐harm for the first time during the pandemic. People with these risk factors may need particular attention during future pandemics to enable early identification of new psychiatric symptoms.