Previous research on union participation has been disjointed, with no clear consensus on the definition and nature of participation.Additionally, few studies have examined how participation changes over time, with those that have finding mixed results regarding its stability. We propose that these mixed and inconsistent findings are due largely to past research focusing on overall levels of participation, ignoring differences in how individuals participate. To remedy this, we adopted a person-centered approach to identify different types of union participators. Using a large sample of union members, we conducted latent transition analysis and found six union participator classes: high participators, leadership participators, formal union promoters, informal union promoters, silent supporters, and non-participators. In addition, we examined how individuals changed membership across two time points (separated by 6 years), antecedents of class membership (role tenure and union commitment), and outcomes (freerider intentions and actual financial contributions to the union's political action fund). The six classes differed uniquely, in terms of the ways people participate, changes in how people participate over time, what predicted class membership, and how class membership impacts two outcomes. The current study demonstrates that person-centered approaches can both clarify previous conflicting findings within the participation literature and predict meaningful outcomes. K E Y W O R D S latent transition analysis, person-centered analysis, unions, union commitment, union participation Personnel Psychology. 2020;73:271-304.wileyonlinelibrary.com/journal/peps