Introduction In recent decades, the labour market has evolved into temporary employment, part-time work, and long-term unemployment, especially affecting young population and women. Transitions between states during working life could affect mental health.

Objectives To assess the relationship between early working life (EWL) patterns and the future course of sickness absence (SA) due to mental disorders.

Methods Cohort study of a working sample between 18 and 28 years of age, residents in Catalonia, with at least one episode of SA due to a mental disorder between 2012 and 2014. Reconstruction of individual working life trajectories previous to the SA were carried out by sequence analysis based on four work-related states (permanent, temporary contract, unemployment and without social security coverage). By optimal matching, patterns were identified out of clustering similar working trajectories. Identification of SA trajectories were made by latent class growth modelling analysis. Adjusted multinomial logistic regression models were applied to assess the relationship between early working life patterns and SA trajectories.

Results Among men, fluctuating (aOR 1.25[95% CI: 0.57–2.74]) or delayed (aOR 1.79 [95% CI: 0.59–5.41]) entry into the labour market showed a trend towards a middle stable accumulation of SA days. In women, an increasing permanent and fluctuating employment pattern (aOR 2.41 [95% CI: 1.01–5.75]) at the beginning of their EWL was related to a decreased accumulation of future days on SA due to mental disorders (aOR 2.08 [95% CI: 1.18–3.66]) rather than to a low stable trajectory.

Conclusions An unstable early working life built on a high number of transitions between temporary contracts, unemployment and lack of social security coverage states is related to a future worse SA course due to mental diagnosis.