ObjectiveThis study examined the relationship between precarious employment (PE) and mental well‐being, focusing on age‐specific interactions.MethodsNationally representative Korean workers (N = 29,961) were surveyed between 2020 and 2021 to collect data on multidimensional PE (categorized as low, moderate, or high) and the WHO‐5 well‐being index. Workers' ages were classified as young (<35 years), middle‐aged (35–54 years), and older (≥55 years). Logistic regression was performed to estimate the odds ratios (ORs) and 95% confidence intervals (CIs). The interaction between PE and age on well‐being was examined by including interaction terms in the regression models.ResultsThe prevalence of poor well‐being was 25%, 29%, and 39% for low, moderate, and high precariousness, respectively, whereas it was 26%, 30%, and 39% for young, middle‐aged, and older workers, respectively. In the overall sample, the OR (95% CI) of the association between PE and poor well‐being was 1.24 (1.17–1.32) for moderate and 1.54 (1.43–1.65) for high precariousness, compared with low precariousness. There was a significant interaction between old age and PE on the odds of poor well‐being. Compared with young workers with low PE, middle‐aged workers with high PE (OR: 1.85, 95% CI: 1.62–2.10) and older workers with high PE (OR: 2.10, 95% CI: 1.83–2.40) exhibited increased odds of having poor mental well‐being.ConclusionPE serves as a social determinant of older workers' psychological well‐being. Policy interventions are required to protect older workers' psychological well‐being.