Canadian households experienced unexpected changes in their economic well-being during the COVID-19 pandemic. The extent of the impact of the pandemic on household debt and its effect on health and mental health remains unknown. The aim of the study was to examine the associations of change in household debt due to COVID-19 with serious psychological distress (SPD) and general health measures. Data were from the 2020 Monitor study, a repeated cross-sectional survey of adults 18 years and older in Ontario, Canada. The 2020 cycle employed a web-based panel survey of 3,033 adults. The survey included measures of change in household debt due to the COVID-19 pandemic, mental and general health. Odds ratios (OR) were estimated from logistic regression models accounting for sociodemographic factors. Overall, 17.5% of respondents reported that their household debt increased due to the COVID-19 pandemic. Such an increase in household debt was significantly associated with SPD (OR = 2.92, 95% CI, 2.05-4.16), fair/poor mental health (OR = 2.02, 95% CI, 1.59-2.56), frequent mental distress days (OR = 1.80, 95% CI, 1.31-2.48), fair/poor general health (OR = 1.93, 95% CI, 1.47-2.52), and suicidal ideation (OR = 3.71, 95% CI, 2.41-5.70) after adjusting for potential confounders including education, income and employment. Household debt during the COVID-19 pandemic is an important determinant of health. Individuals who reported an increase in household debt due to COVID-19 were more likely to report serious mental health concerns including suicidal ideation. This suggests that debt-related interventions may be needed to alleviate the adverse effects of indebtedness on health.