While the development of hagiography over time has long attracted the attention of medievalists, scholars have not fully explored the critical role of the liturgy in prompting and transmitting these changes. This dissertation examines the liturgies for the patron saints of three musical and ecclesiastical centers in medieval Aquitaine: the cathedrals of Saint-Trophime in Arles, Saint-Just-et-Saint-Pasteur in Narbonne, and Saint-Étienne in Toulouse. Through the music, texts, and ritual actions of the liturgy, the clerical communities of these three institutions reinforced some aspects of their patron saint's legendary biography and modified others. Yet the process unfolded differently at each cathedral, revealing the particular preferences of the canons of each community as well as their changing circumstances during the Middle Ages. In Arles, the office for St. Trophime, which was likely composed at the cathedral, shows dramatic changes in the saint's hagiography. The clerics in Narbonne also composed an office for their patron saints but did not substantially change the details of Justus and Pastor's legendary biography. In Toulouse, the canons selected from among the preexisting repertoire of chants and texts available for St. Stephen, crafting liturgies that were particular to Saint-Étienne within a clearly Aquitanian context. By revealing the ways in which the clerics of Saint-Trophime, Saint-Just, and Saint-Étienne shaped the legendary biographies of their patron saints, my work provides new insights into the ways in which clerical communities throughout Latin Christendom shaped and reshaped the hagiographic portraits of their patron saints through the creation, compilation, and celebration of new liturgies.