Women remain under-represented in top leadership positions in work organizations, a reality that reflects a variety of barriers that create a glass ceiling effect. However, some women do attain top leadership positions, leading scholars to probe under what conditions women are promoted despite seemingly intractable and well-documented barriers. Previous scholarship tends to posit individual-level explanations, suggesting either that women who attain top leadership positions are exceptional or that potential women leaders lack key qualities, such as assertiveness. Much less scholarship has explored institutional-level mechanisms that may increase women's ascension to top positions. This analysis seeks to fill this gap by testing three institutional-level theories that may shape women's access to and tenure in top positions: the glass cliff, decision-maker diversity, and the saviour effect. To test these theories we rely on a dataset that includes all CEO transitions in Fortune 500 companies over a 20-year period. Contrary to the predictions of the glass cliff, we find that diversity among decision makers — not firm performance — significantly increases women's likelihood of being promoted to top leadership positions. We also find, contrary to the predictions of the saviour effect, that diversity among decision makers increases women leaders' tenure as CEOs regardless of firm performance. By identifying contextual factors that increase women's mobility, the paper makes an important contribution to the processes that shape and reproduce gender inequality in work organizations.