Despite the thousands of Christians killed in early modern missions across the world, studies of Christian martyrdom have traditionally been preoccupied with the European context, or otherwise confined to regionalised studies of encounters. This thesis examines Catholic missionary writings on violence and executions in a global comparative context, drawing upon examples from England, Japan, Paraguay and New France. It argues that martyrdom functioned not only as a description of an event or an interpretative category but that it represented a missionary world view. Martyrdom constituted a language of faith and sanctified suffering, as well as a marker of renewed Catholic priestly identity. This was possible because martyrdom was a conduit of the principal biblical teachings and mysteries, and held a revered place in church tradition. The thesis highlights its importance as an intrinsic part of missionary spirituality: martyrdom was a desirable outcome of mission, while mission was seen as a form of martyrdom. This study also compares alternative perspectives, revealing the common views of Catholic missionaries as subversive, rival sources of authority, and analyses attitudes toward death and violence in the early modern world. It examines how missionaries wrote about persecution, exploring the implications of the consoling and edifying purposes of these texts in times of difficulty, and the ways in which the concept of martyrdom was used by converts. It argues that missionaries viewed martyrdom as a pastoral responsibility, an act of worship and literal sacrifice for their communities. Finally, the thesis explores how missionaries interpreted encounters with Protestant empires, highlighting their interconnectedness, and the role of translations in creating a truly universal church. It argues that the global experience of martyrdom was central to the story of early modern Catholicism.