Although researchers have suggested that the social context in exercise settings is linked to individuals’ physical activity motivation and potential exercise-related outcomes, few research designs have examined the nuance of those relationships. The purpose of this study was to examine longitudinally the relationships between the motivational climate of a fitness center and members’ exercise experiences, using an intervention designed from achievement goal perspective theory and self-determination theory. Using a half-longitudinal structural equation model, we modeled members’ perceptions of the motivational climate, basic psychological needs, exercise motivation, and exercise experiences (including commitment to exercise, life satisfaction, and body image) pre- and post-intervention The model revealed significant latent mean differences for post-intervention constructs, with participants experiencing a more positive motivational climate, higher competence and relatedness, intrinsic motivation, commitment, and life satisfaction. The final mediation model demonstrated tenable fit, suggesting that perceptions of climate have significant direct and indirect effects on commitment, life satisfaction, and body image. Our study supports the view that perceptions of the motivational climate as caring and task-involving contribute to an advantageous social context for exercise where basic psychological needs are nurtured; intrinsic motivation is fostered; and individuals experience well-being benefits, including increased life satisfaction. Short and targeted caring and task-involving climate training with fitness center staff may result in members’ perceiving a significant change in the motivational climate. Further randomized controlled studies should confirm these hypotheses.