Objectives: Clarify the association between income group and oral health-related quality of life. Methods: Data were used from a nationally representative online survey with n = 3075 individuals. It was conducted in late Summer 2021. The established Oral Health Impact Profile (OHIP-G5) was used to measure oral health-related quality of life. The income group (household net income) was used as key independent variable. It was adjusted for several covariates. Full-information maximum likelihood was used to address missing values. Results: Individuals in the lowest income decile had a lower oral health-related quality of life (Cohen’s d = −0.34) compared to individuals in the second to ninth income deciles. Individuals in the highest income decile had a higher oral health-related quality of life (Cohen’s d = 0.20) compared to individuals in the second to ninth income deciles. Consequently, there was a medium difference (Cohen’s d = 0.53) between individuals in the lowest income decile and individuals in the highest income decile. Additionally, multiple linear regressions showed significant differences between individuals in the lowest income decile and individuals in the second to ninth income deciles (β = 0.72, p < 0.01). In contrast, only marginal significant differences were identified between individuals in the second to ninth income deciles and individuals in the highest income decile (β = −0.28, p < 0.10). Conclusions: The current study particularly stressed the association between low income and low oral health-related quality of life in the general adult population. Increasing oral health-related quality of life in individuals with low income is a major issue which should be targeted.