Background: 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. Aim: 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. Methods: 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. Results: 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. Conclusions: 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.