Women are consistently under-represented in the upper echelons of the bureaucracy. In this paper, we investigate when and why women’s careers stagnate using comprehensive data on personnel records on all civil servants employed in the Danish ministerial bureaucracy from 1999 through 2019. We show that women’s careers stagnate at the earliest possible stage: a lower proportion of women ever enter into the lowest level of management, and when they do, they do so at a higher age than men. This exacerbates gender imbalance at all higher levels of management. Next, we use a difference-in-differences design to show that women’s probability of entering the lowest level of management drops significantly compared to men, when they get a man as the leader of their unit. The arrival of a woman as the unit leader does not have a similar positive effect. Further heterogeneity analyses show that the negative effect on women’s careers is concentrated among women younger than 45 years of age and in units where there is a high proportion of women managers. Having a woman as the minister only suppresses the effect at higher levels of management. There are no differences between governments of different partisanship.