Guillermo Trejo is Associate Professor of Political Science at the University of Notre Dame and Faculty Fellow at the Kellogg Institute for International Studies. He was previously on the faculty at Duke University and at the Centro de Investigacin y Docencia Econmicas (CIDE) in Mexico City.

Trejo's research focuses on collective action and social protest, armed insurgencies and political violence, and religion and ethnic identities in authoritarian regimes and new democracies. He is the author of "Popular Movements in Autocracies: Religion, Repression and Indigenous Collective Action in Mexico" (Cambridge University Press, 2012). His work has been featured in the American Political Science Review, the Journal of Latin American Studies and Poltica y gobierno. Trejos doctoral dissertation received the 2006 Mancur Olson Award from the Political Economy Section of the American Political Science Association and his research on religious competition and ethnic mobilization in Latin America received the 2011 Jack Walker Outstanding Article Award from the APSA Political Organizations and Parties Section.

Trejo is currently working on a new research agenda on organized crime and violence in new democracies. Whereas his previous work sought to explain the rise and transformation of peaceful social movements into armed insurgencies and their impact on democratization, his current research seeks to explain the rise of organized crime, its transformation into criminal insurgencies, and its impact on the quality of democracy. He is working on a book provisionally entitled Votes, Drugs, and Violence: Democratization and Organized Crime in Latin America.