This article investigates the role of family socio-economic status (SES) as a buffer for adolescents with mental health disorders (MHDs) against entering precarious school-to-work trajectories. We follow a cohort born in Norway in 1992 from the age of 16–25 using data from administrative registers. We find that externalizing disorders, to a higher degree than internalizing disorders (registered in the 16–18 age range), are associated with subsequent precarious school-to-work trajectories (measured from January 2011 to December 2017) for both genders. In boys, high family SES seems to buffer the negative impact of externalizing disorders on entering precarious school-to-work trajectories, but not for internalizing disorders. In contrast, in girls, high-SES families partly buffer the negative impact of internalizing disorders, but not for externalizing disorders. Thus, this paper broadens the current perspective on how the impact of MHDs on entering school-to-work trajectories is interrelated with social class and gender.