Transparency is expected to strengthen electoral accountability. Yet, initiatives disseminating politician performance information directly prior to elections have reported disappointing results. We argue that to be effective transparency needs to be sustained: the dissemination of politician performance information needs to occur early, regularly, and predictably throughout the term. Using a formal model of electoral accountability under non-programmatic and uneven party competition, we study how sustained transparency impacts a string of decisions by various actors in advance of elections: incumbents’ running choices, party nomination strategies, and potential challengers’ entry decisions. We show how these effects shape the candidate slate and ultimately electoral outcomes, conditional on incumbent performance and the incumbent party’s relative strength. We test our theory using a field experiment involving 354 subnational constituencies in Uganda, and find robust support to the idea that sustained transparency can improve electoral accountability even in weakly institutionalized electoral settings.