This chapter underscores the role of employment precariousness as a powerful social determinant of youth mental health, explaining how and why young people are both more frequently exposed to employment precariousness compared to other population groups, and more deeply affected by its mental health consequences. The chapter contributes to challenging individualized interpretations of the youth mental health crisis to emphasize how employment precariousness constitutes a key mechanism through which broader structural labor-market features are internalized as psychological distress among the youth. Such process is explained, first, by adopting a life course perspective, situating employment precariousness and youth mental health at the intersection of age (the life stage during which transitions to autonomy and adulthood take place), historical period (neoliberal transformations in labor markets and society), and generational cohort (the particular stance upon which both overlap). Second, the chapter presents the process by which youth employment precariousness’ effects extend beyond work, operating as both a symptom and a driver of wider precarity or ontological insecurity. The chapter describes the snowball effect of employment precariousness on youth life trajectories, emphasizing its cumulative impact on both present and future mental health. Four core pathways through which employment precariousness affects youth mental health are presented: exposure to harmful working conditions, heightened economic insecurity, difficulties in achieving residential and family transitions, and uncertainty about the future. Finally, the chapter highlights how employment precariousness plays a critical role in reproducing and amplifying social inequalities such as gender, class, race, or migration background in youth mental health, and concludes outlining key policy implications.