Objectives: Aims of this study were to Schmitt (Advances in Life Course Research, 2021, 47: 100402) analyze the association of working poverty with mental and physical health-related quality of life and (Wang and Ford, J Organ Behav, 2020, 41 (9): 895–914) to explain these associations by behavior-related factors (heavy drinking, smoking status, body mass index), socioeconomic insecurity (deprivation in living standards, economic worries), and mental working conditions (effort-reward imbalance, job insecurity). Methods: A total of 11,500 employees aged 17–67 from the German Socioeconomic Panel (2014, 2015, and 2016) were used, and mediation analyses with inverse odds weighting stratified by gender were conducted. Results: Working poverty was significantly associated with both outcomes for both genders. Deprivation in living standards contributed the most to differences in mental health, with a mediated proportion of 60.3% (men) and 44.4% (women). Differences in physical health were significantly mediated by inadequate living standards in women, with a mediated proportion of 73.7%, whereas none of the mediators considered were significant in men. Conclusion: Indicators of socioeconomic insecurity contributed most to the association of working poverty with mental and physical health. Results highlight the relevance of policy initiatives to strengthen the socioeconomic living conditions of the working poor.