Household mortgage debt unleashed devastating consequences for the global economy in 2007–2008. Despite the growing importance of household debt in financial markets, international political economy and comparative political economy have not theorized why it varies so much across Europe. We argue that variation in household debt can be explained by the intersection of two domestic institutions: labor market institutions (and by extension the welfare state) that enable households to withstand negative employment/income shocks, and mortgage finance institutions that govern households’ credit access. We empirically demonstrate via a panel analysis of 17 advanced capitalist democracies that the impact of these institutions on household debt is co-dependent. Strong collective bargaining institutions (and generous welfare states), which protect borrowers from income and employment insecurity, are associated with higher household indebtedness, but only if housing finance institutions that encourage mortgage lending are present (i.e. in Scandinavia and the Netherlands). In contrast, liberal (financialized) economies have comparatively lower household indebtedness because their labor market institutions inhibit income security for borrowers. As household debt becomes more central to comparative political economy, our findings suggest that scholars who study financialization need to integrate labor market (and welfare state) institutions into their analysis to understand how domestic financial systems function.