Career insecurity is a central topic in career research because many career paths are characterized by high levels of uncertainty. In academia, individuals face not only high levels of insecurity in the early career phase but also the responsibility of managing their careers by themselves. Building on the motivational theory of life-span development and the social cognitive theory of self-regulation, this longitudinal study investigates the relationship between perceived career insecurity, work-related self-management, and occupational self-efficacy beliefs based on a sample of 3118 PhD students and PhD holders. We employed the random intercept cross-lagged panel model (RI-CLPM) to separate between-person effects from within-person effects across eight measurement points (6-month time intervals). At the between-person level, career insecurity was negatively correlated with self-management and self-efficacy. At the within-person level, (a) increases in self-management and self-efficacy predicted decreases in subsequent career insecurity, and (b) increases in career insecurity predicted decreases in subsequent self-management and self-efficacy. Mediation analyses showed self-management to reduce career insecurity via increases in self-efficacy. •Eight-wave longitudinal study with 3118 young scientists•Self-management, self-efficacy, and career insecurity relate at the within level.•Increases in self-management/self-efficacy predict decreases in career insecurity.•Increases in career insecurity predict decreases in self-management/self-efficacy.•Self-management reduces career insecurity via increases in self-efficacy.