Trajectory studies of the COVID-19 pandemic have described patterns of symptoms over time. Yet, few have examined whether social determinants of health predict the progression of depression and anxiety symptoms during COVID-19 or identified which social determinants worsen symptom trajectories. Using a racially, ethnically, and linguistically diverse sample of adults participating in a randomized clinical trial with pre-existing moderate to severe depression and/or anxiety symptoms, we compare symptom patterns before and during COVID-19; characterize symptom trajectories over a 20-week follow-up period; and evaluate whether social determinants are associated with within- and between- person differences in symptom trajectories. Data were collected before and during COVID-19 in Massachusetts and North Carolina. On average, depression and anxiety symptoms did not seem to worsen during the pandemic compared to pre-pandemic. During COVID-19, anxiety scores at follow-up were higher for participants with baseline food insecurity (vs no food insecurity). Depression scores at follow-up were higher for participants with food insecurity and for those with utilities insecurity (vs no insecurity). Participants with child or family care responsibilities at baseline had depression symptoms decreasing at a slower rate than those without these responsibilities. We discuss the important implications of these findings.