Daisaku Ikeda is the Buddhist leader of one of the most visible religious movements today, the Soka Gakkai International (SGI). In this thesis, the main research question concerns the peace philosophy of Ikeda and its contribution to peace theory. Daisaku Ikeda and the SGI have been the subject of several scholarly studies in the fields of religious history and sociology. The focus of this research is on the significance of Ikeda's contributions in the field of peace studies, where his work has not yet been the subject of systematic investigation. It is argued that the originality of Ikeda's philosophy of peace resides in two main elements. First, the starting point is consistently human life and its potential for peace and happiness, not the omnipresence of conflict. Second, he offers a coherent system linking the individual, dialogical and global levels, which can be represented as a triangle made of three conceptual frameworks, that of Humanistic Psychology (Human Revolution), Communicative Rationality (Dialogue) and Cosmopolitan Democracy (Global Civilization). It is also argued that while being inspired by Ikeda's Buddhist spirituality and his loyalty to his mentor Josei Toda, this secular humanist approach to peace offers an effective and original way for all people to participate in the construction of a better world, regardless of their religious or ideological affiliation, social background or cultural practices.