Brian Catlos studies the dynamics of the social, economic and cultural interaction of ethno-religious groups in the Medieval Mediterranean, especially Christians, Muslims, and Jews in Iberia. He received a B.A. in History and Philosophy (1994) from the University of Toronto (Canada), and an M.A. (1996) and Ph.D. (2000) in Medieval Studies (History) from the Centre for Medieval Studies. His dissertation, "The Victors and the Vanquished: Christians and Muslims of the Ebro Valley, ss. XI-XIII" was awarded the Governor-General of Canada's Gold Medal as well as the First Leonard E. Boyle Dissertation Prize (Canadian Society of Medievalists). He has been a postdoctoral fellow of the Social Sciences and Humanities Research Council of Canada, a visiting scholar at the Institute for Medieval History (Boston University), the Institut Milà i Fontanals (Consejo Superior de Investigaciones Cientificas, Barcelona) and the Institut d'Estudis Catalans (Barcelona).

Until 2012, he was an Associate Professor of History at the University of California Santa Cruz (cross-appointed to Jewish Studies). In 2009-10 was a Visiting Associate Professor of Spanish and Portuguese at the University of Colorado at Boulder. Presently he is an Associate Professor (and Director of Undergraduate Studies) at CU Boulder (affiliated with History, Humanities and Jewish Studies), a Research Associate in Humanities at the University of California Santa Cruz , a project member at the Institut Milà i Fontanals (CSIC, Barcelona), and an external faculty member of the Università di Messina (Italy). Recently, he collaborated in a multi-year project sponsored by the Université de Paris, entitled "Elites rurales méditerranéennes au Moyen Âge (Ve-XVe siècle)." He regularly delivers lectures, talks and conference papers in North America, and Europe (over 90 to date), and organizes conferences and panels at academic meetings (over 80 to date).

He has been awarded grants, fellowships, honors and prizes from the Spanish Ministry of Exterior, the Spanish Ministry of Education, the Catalan government, the University of California, the University of Toronto, the Government of Ontario, the IODE , the Canadian Association of University Teachers, and the American Historical Association. In 2005 he received a UC President's Research Fellowship in the Humanities in support of an archival project, "Conflicts of Interest: Minority Administrative Elites in 14th-Century Aragon." In 2006 his book The Victors and the Vanquished: Christians and Muslims of Catalonia and Aragon, 1050-1300 (Cambridge, 2004) was honored by the American Historical Association with the John E. Fagg Prize, and it was been selected by the American Historical Association for the "Premio del Rey" in 2007. A Spanish translation was published in 2009. In 2009–10 he held a research fellowship from the National Endowment for the Humanities. This led to the publication of Muslims of Medieval Latin Christendom, ca. 1050-1614 ( Cambridge University Press, 2014), a book that received the Middle East Studies Association Albert Hourani Prize in 2014 and the Medieval Academy of America's Haskins Medal in 2018. In 2022 it was released in Turkish. Infidel Kings and Unholy Warriors: Power, Faith and Violence in the Age of Crusade and Jihad, a "cross over" book, meant for a popular as well as a scholarly audience was published by Farrar, Straus & Giroux in August 2014. It was a Publishers' Weekly Pick of the Week, and received a starred review in Booklist as well as honorable mention in the 2015 American Publishers PROSE Awards for Professional and Scholarly Excellence, and has been published in Dutch translation. His book, Kingdoms of Faith: A New History of Islamic Spain (Basic: 2018) received a starred review in Library Journal and is being translated into German, Spanish, Simpllified Chinese, Complex Chinese, Korean and Polish, and will soon be out in Russian. In 2022 together with Thomas Burman and Mark Meyerson, he published a textbook, The Sea in the Middle: The Mediterranean World, 650-1650 (Univeristy of California) and a source reader, Texts from the Middle: Documents from the Mediterranean World, 650–1650 (University of California).    

Since 2008 he has been co-director of the Mediterranean Seminar, an independent forum for research and pedagogy in the emerging field of Mediterranean Studies, which enjoys the collaboration and support of the University of California, the Universitat Pompeu Fabra (Barcelona), the Institució Milà i Fontanals, and a number of other institutions in Europe and North America. The Mediterranean Seminar has an editorial and advisory board made up of leading authorities and new scholars in a range of disciplines, and over 600 affiliates worldwide. Programs Catlos and Kinoshita have co-directed under the aegis of the Mediterranean Seminar include a long-standing research group at UCSC, a 14-week Residential Research Group at the UC Humanities Research Group, a France-Berkeley exchange program with the Université de Paris and the Université Marc Bloch, four NEH Summer Institutes for College and University Professors (2008, 2010, 2012, and 2015), and a workshop at the 13th Mediterranean Research Meeting, hosted by the European University Institute (Florence & Montecatini Terme, Italy), as well as many other programs. They established the UCSC Center for Mediterranean Studies in 2009 and the Mediterranean Consortium, a loose organization of Mediterranean Studies programs around the world. In 2010 he began as PI and co-Director (with Kinoshita) of a 5-year Multi-Campus Research Project in Mediterranean Studies, which received a $500K grant from the University of California. The core of the MRP Program consisted of a series of workshops, conferences and other activities aimed at fostering national and international scholarly collaboration, original research and pedagogical development. The grant concluded in June 2015 after which the Seminar shifted administratively to CU Boulder and has continued as a self-funding project. In 2012 Palgrave/MacMillan asked Catlos and Kinoshita to launch a new series, Mediterranean Perspectives, which they now edit. In 2010 he received an Innovative Seed Grant from the University of Colorado at Boulder to launch the CU Mediterranean Studies Group, and in collaboration with the UC project and the Mediterranean Seminar. The Mediterranean Seminar has formed liaisons with a number of North American and European projects and institutions and regularly sponsors, organizes and co-organizes panels at international conferences and meetings of scholarly societies.

In 2008 he was elected President of the American Academy of Research Historians of Medieval Spain and served through 2010, during which time he oversaw a modernization of the payment system and set up a new website. He also served on the AHA's Premio del Rey Prize committee, and served as Late Medieval Book Review editor for the Medieval Academy's journal, Speculum. He serves on the editorial board for a number of journals and publication series, including: "Anejos" del Anuario de Estudios Medievales, postmedieval: a journal of medieval cultural studies, Mediterranean Chronicle, Aragón en la Edad Media, Journal of Medieval Iberian Studies, American Journal of Mediterranean Studies, and Imago in Specvlo. He has carried out pre-publication manuscript and proposal reviews for Cambridge University Press, Viator, Chicago University Press, Journal of Medieval Iberian Studies, Columbia University Press, Longman Publishers, La Corónica, University of North Carolina Press, Enslow Publishers, Mediterranean Studies, and University of California Press among others.

In 2010 he accepted a position as Associate Professor of Religious Studies at the University of Colorado at Boulder, and established cross-appointments in Asian Languages and Civilizations, History, Humanities, Ethnic Studies and the Jewish Studies program. He was promoted to the rank of Professor in 2014. In July 2012 he resigned his position as Associate Professor of History at UCSC, having accepted an appointment as a Research Associate of the Humanities Division. This was renewed in 2014. He continues as co-Director of the UCSC Center for Mediterranean Studies, and the UC Mediterranean Studies Multi-Campus Research Project. In 2012 he was also appointed an associate faculty of the Center for Medieval and Renaissance Studies at the University of California at Los Angeles. He accepted an invitation to join the Executive of the Journal for Medieval Iberian Studies, and resigned as Book Review Editor of Speculum. In 2015 he received an Award for Excellence in Research, Scholarly, and Creative Work from the Boulder Faculty Association, and in 2017, the same body presented him with an Award for Excellence in Leadership & Service.

In addition to his monographs he has co-edited a special edition of Scripta Mediterranea, titled "New Approaches to the Study of Muslims in the Medieval West," and co-edited a special edition of Medieval Encounters on medieval disputation, and edited one of the manuscript versions of the Fuero General de Navarra. With Sharon Kinoshita he co-edited Can We Talk Mediterranean? Considerations on an Emerging Paradigm in Medieval and Early Modern Studies(Palgrave: 2017)— a volume based on the Spring 2011 workshop/conference held by the UC Mediterranean Studies MRP and the CU Mediterranean Studies Group. He has published 17 journal articles and book chapters, over 50 short articles and encyclopedia entries, and over 40 book reviews. His article "To Catch a Spy: The Case of Zayn al-Din and Ibn Dukan" [Medieval Encounters 2 (1996)] was translated into Arabic, and "The de Reys (1220–1501): The Evolution of a "Middle-Class" Muslim Family in Christian Aragon" [Viator 40 (2009)] was awarded the Bishko Prize in 2009 by the Association for Spanish and Portuguese Historical Studies. In 2009 he edited a festschrift in honor of this dissertation supervisor, Worlds of History and Economics. Essays in Honour of Andrew M. Watson (Valencia: Universitat de Valencia). His essay, ""Accursed, Superior Men": Political Power and Ethno-religious Minorities in the Diverse Medieval Mediterranean" was co-awared (together with a work by Thomas F. Glick), the 47th Annual Walter Prescott Webb Essay Prize from the University of Texas at Arlington, and was be published in Comparative Studies of Society and History.

A number of articles are at press, and several book projects are in progress, including An Age of Convergence: Christians, Muslims and Jews in the Pre-Modern Mediterranean, and James the Conqueror. A Crusader King in an Age of Faith and Reason. Other current undertakings include a number shorter archival studies on the Muslims and Jews of late Medieval Christian Spain, various projects connected to Mediterranean Studies. 

Since the 1980s he has travelled extensively on five continents (once hitch-hiking from London to Istanbul and back) and has lived, worked and studied in North America, Europe, the Middle East and Latin America. He also writes, contributes to and consults for travel publications, and is involved in documentary film. He currently lives outside Boulder, Colorado and in Barcelona, Spain.