ObjectiveSocial and economic marginalizations have been associated with inferior health outcomes in Canada. Our objective was to describe the relationship between neighbourhood marginalization and COVID-19 outcomes among patients presenting to Canadian emergency departments (ED).MethodsWe conducted an observational study among consecutive COVID-19 patients recruited from 47 hospitals participating in the Canadian COVID-19 ED Rapid Response Network (CCEDRRN) between March 3, 2020, and July 24, 2022. We linked data with the Canadian Marginalization Index (CAN-Marg). We used multivariable, multi-level logistic regression models to understand the association between dimensions of neighbourhood marginalization, and severe COVID-19 and in-hospital mortality.ResultsThere were 55,588 eligible patients. Those from neighbourhoods with a higher proportion of recent immigrants (OR = 0.86 per unit increase [0.81, 0.92]), lower workforce participation (OR = 0.84 per unit increase [0.75, 0.94]), and more housing insecurity (OR = 0.81 per unit increase [0.77, 0.86]) were less likely to present to EDs with severe COVID-19. However, patients from materially marginalized neighbourhoods had increased odds of dying in hospital (OR = 1.19 per unit increase [95% CI 1.09, 1.30]) compared to patients from less materially marginalized neighbourhoods. Patients living in neighbourhoods with a higher proportion of recent immigrants (OR = 0.83 per unit increase [0.78, 0.91]) and lower participation in the workforce (OR = 0.77 per unit increase [0.66, 0.87]) experienced lower odds of dying.ConclusionDespite no association with severe COVID-19 at ED presentation, the only marginalization domain associated with in-hospital mortality was material deprivation. Our findings present insights on ED-seeking behaviour, hospital access, and care that population studies could not.