•We examined the association between working hours and the onset of suicidal ideation among female workers in Korea.•Those working ≥55 h per week had a 1.7-fold increased risk of developing suicidal ideation than those 35–40 h per week.•A pronounced association was observed among individuals with low-income levels or those employed in blue-collar jobs.•Our findings suggest that policy efforts are required to promote the mental health of workers exposed to long working hours. Long working hours and overwork have recently emerged as pressing public health concerns. We explored the association between long working hours and suicidal ideation in female workers. A total of 8017 women (24,331 observations) from the fourth to eighth waves of the Korean Longitudinal Survey of Women and Families (2012–2020) were analyzed. To address the repeated measurements within each participant, we employed a generalized estimating equation to estimate the odds ratio (OR) and 95% confidence intervals (CIs). The prevalence of suicidal ideation was 1.9% for those working 35–40 h/week and 4.4% for those working ≥55 h/week. Compared to individuals working 35–40 h/week, those working ≥55 h/week were more likely to experience concurrent suicidal ideation (OR 95% CI:1.85 1.43–2.39). The OR (95% CI) of the association between long working hours and onset of suicidal ideation in the subsequent wave was 1.69 (1.20–2.38) for ≥55 h/week. In subgroup analysis, this association was pronounced among workers with low-income levels (OR 95% CI: 1.97 1.29–3.02) and blue-collar occupations (OR 95% CI: 2.27 1.41–3.66). Policy efforts are required to protect the mental health of female workers exposed to long working hours.