Basic psychological needs (BPN) are a construct that helps clarify the psychological mechanism to reach desirable outcomes for youth athletes. When BPN are undermined, people should be less likely to thrive. As mental toughness (MT) can reduce the negative effects of stressors, MT may buffer the negative effects of maladaptive motivation. This study investigated the mediating role of thriving on the relationships between BPN thwarting and important outcomes for youth athletes’ positive functioning. It also examined the buffering effects of MT. One hundred eighty-eight Canadian youth athletes (M age = 15.51) answered an online survey. The results demonstrated that thriving was a significant mediator, and the indirect relationships were moderated by MT. The indirect associations were nonsignificant for youth with high MT. The findings demonstrated that MT might decrease the negative impacts of BPN thwarting on thriving and important outcomes for young athletes.