The aim of the present study is to provide a deeper understanding of how autonomy-supportive leadership affects volunteer motivation by taking volunteers’ individual differences into account. For this purpose, self-determination theory (SDT) was utilized because this conceptual framework considers both the social context (i.e., autonomy-supportive leadership) and individual differences (i.e., causality orientations) as antecedents of motivation. Causality orientations alter the way individuals perceive their social context as either autonomy-supportive or controlling (i.e., autonomy orientation or control orientation, respectively). Therefore, it is hypothesized that both types of causality orientations serve as moderators of the relationship between autonomy-supportive leadership and volunteer motivation. The hypotheses were tested on N = 1,979 volunteers. The results revealed that the relationship between autonomy-supportive leadership and volunteer motivation varied as a function of the strength of autonomy and control orientation. The importance of the moderating role of individual differences on volunteer motivation is discussed.