Avoidable mortality (AM) is a health indicator used to examine trends in avoidable deaths amenable to public health and medical interventions. AM is more likely amongst marginalized populations. Our objective was to examine trends in AM rates by level of neighborhood marginalization. Decedents under age 75 years in Ontario from 1993 to 2014 (n = 691,453) were assigned to a quintile-level of each Ontario Marginalization (ON-Marg) Index dimension: material deprivation, residential instability, dependency, and ethnic concentration. We calculated ON-Marg Index dimension and quintile specific age- and sex-standardized AM incidence rates. We then calculated annual AM rate ratios between the most (Q5) and least (Q1) marginalized quintiles for each ON-Marg dimension. To describe the inequity gap in AM over time we calculated the absolute difference in the Q5/Q1 rate ratio between 2014 and 1993 for each dimension. AM rates in Ontario were almost halved (48.6%) from 1993 to 2014 (216 vs. 111 per 100,000 population). This decline was greater for treatable AM (75 vs. 36 per 100,000 population) than preventable AM (128 vs. 88 per 100,000 population). The inequity gap in AM Q5/Q1 rate ratios (RR) between 1993 and 2014 widened for all marginalization dimensions: dependency (RR 2.11-2.58), ethnic concentration (RR 0.59-0.48), material deprivation (RR 1.63-2.23), and residential instability (RR 2.01-2.43). To attain further declines in AM, policymakers and governments must address AM due to preventable deaths in neighborhoods highly marginalized by dependency, material deprivation, and residential instability.