Effective altruism’s identity as both a philosophy and a social movement requires effective altruists to consider which philosophical commitments are essential, such that one must embrace them in order to count as an effective altruist, at least in part in the light of the goal of building a robust social movement capable of advancing its aims. The goal of building a social movement provides a strong reason for effective altruists to embrace an ecumenical set of core commitments. At the same time, there are risks involved in adopting an ecumenical approach to social movement building. In this paper, I develop a view about how effective altruists should characterize the movement’s core philosophical commitments, in light of the challenges of social movement building. I suggest that John Rawls’s idea of an “overlapping consensus” provides a useful model for thinking about the philosophical core and broader structure of the movement.