Volunteer role identity is regarded the direct and proximal cause of sustained volunteerism. Self-determination theory suggests that the quality of motivation greatly affects performance and well-being in various contexts. Therefore, this study investigated cross-lagged effects (over a time period of 16 months) between self-determined and controlled motivation, on the one hand, and two types of volunteer role identities, on the other hand: general role identity (GRI) and organization-specific role identity (OSRI). Analyses confirmed positive time-lagged effects of self-determined motivation on both GRI and OSRI. Time-lagged effects in opposite direction were significantly weaker; only OSRI showed a positive impact on subsequent self-determined motivation. OSRI (but not GRI) also had a positive lagged effect on controlled motivation. Overall, this study supported the idea that self-determined motivation represents a causal antecedent of volunteer role identities.