The current study aimed to examine whether (a) mean differences and changes in athletes’ attachment style predicted psychological need satisfaction within two diverse relational contexts (coach and parent) and well-being, and (b) mean differences and changes in need satisfaction within the two relational contexts predicted well-being. One hundred and ten athletes aged between 15 and 32 years old completed a multisection questionnaire at three time points over a span of 6 months to assess the main study variables. Multilevel modeling revealed that insecure attachment styles (anxious and avoidant) predicted well-being outcomes at the within- and between-person levels. Avoidant attachment predicted need satisfaction within the parent relational context at both levels, and need satisfaction within the coach relational context at the between-person level. Need satisfaction within both relational contexts predicted various well-being outcomes at the between-person level, while need satisfaction within the parent relational context predicted vitality at the within-person level.