Self-determination theory is a well-studied motivational approach applied in education, sports, exercise, health, and work. However, researchers have yet to explore what motivational underpinnings help explain the relationship between group climate and leader responsiveness on well-being. The current study uses SEM to examine the mediation effect of autonomy, competence, and belongingness between student-rated leaders’ perceived responsiveness and group engagement in group participants’ well-being. Results suggest that basic psychological needs have a full mediation role. The relationship with group members is a stronger predictor of need satisfaction than the leader’s responsiveness. Discussions and recommendations are provided.