Union leaders dedicate a significant amount of their time to unions, and in some cases, their entire life. Scholarly literature has made great progress in identifying the individual and mesolevel variables that explain how this type of union participation begins and continues. Yet it has paid little attention to the role played by the national industrial relations system in these processes. Drawing on the concept of “union career,” this article shows that the national regulations and the union power shape the characteristics and development of union leaders’ participation. Based on an in-depth interview program, a survey and a review of the press in Chile, it examines how neoliberal reforms implemented since 1979 changed the resources and opportunities available to workers to assume, manage, and maintain union positions.