The paper examines job quality in South Korea by applying a novel wellbeing-based approach to defining ‘bad jobs’, extending methodology previously validated in European labour markets. The study analyses Korean Working Conditions Survey (2014–2023) data to investigate the relationship between job quality and worker wellbeing. The analysis reveals a significant discontinuity in the marginal effects of job quality on wellbeing at the bottom decile, where improvements yield distinctly larger wellbeing gains for workers moving above this threshold, providing empirical support for this approach to defining ‘bad jobs’. The prevalence of bad jobs shows a declining trend between 2014 and 2023, reflecting both economic growth and policy interventions. While the sectoral distribution of bad jobs shows similarities with European patterns, distinctive features emerge in South Korea’s labour market structure, characterised by the unique role of large business conglomerates (chaebols) and institutional arrangements. This study represents the first application of a wellbeing-based approach to defining bad jobs in an Asian context, demonstrating both its international applicability and the importance of national context in understanding the patterns of bad jobs. The findings carry significant implications for labour market policy in South Korea’s rapidly evolving economy, particularly for addressing persistent disparities in job quality across different segments of the labour market.