Long working hours are associated with cardiovascular and metabolic diseases. This study investigated the relationship between the working hours and dietary qualities and patterns in Korean workers. Data from 24,523 workers were extracted from the Korea National Health and Nutrition Examination Survey, 2013–2021. The Korean Healthy Eating Index (KHEI), which ranges from 0 to 100, with a higher score indicating greater adherence to Korean dietary guidelines and superior dietary quality, was used for dietary assessment. We identified dietary patterns and classified workers using latent profile analysis. Logistic regressions were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Five distinct dietary patterns emerged: healthy diet (24.8%), low-vegetable diet (14.0%), average diet (7.8%), low-fruit diet (31.4%), and poor diet (22.0%). The mean KHEI score was 60.8, with the highest score observed in the healthy diet pattern (71.3) and the lowest, in the poor diet pattern (50.0). Compared with working 35–40 h/week, working ≥55 h/week was negatively associated with KHEI scores (β: -1.08; 95% CI: −1.67, −0.49). Those working ≥55 h/week were less likely to have a healthy diet pattern (OR: 0.81; 95% CI: 0.72, 0.91) and more likely to have a low-fruit diet (OR: 1.36; 95% CI: 1.20, 1.55) or poor diet pattern (OR: 1.23; 95% CI: 1.05, 1.43) compared with those working 35–40 h/week. Long working hours are associated with undesirable dietary quality and patterns. Policy interventions aimed at enhancing dietary quality are needed to alleviate the health burdens associated with long working hours. •We explored how working hours are related to dietary quality and patterns in Korean workers.•This study used the Korean Healthy Eating Index (KHEI) and latent profile analysis.•Five diet patterns emerged: healthy, low vegetables, average, low fruits, poor diet.•Working ≥55 h/week was associated with decreased KHEI score.•Those working ≥55 h/week were more likely to have poor dietary patterns.