Weight bias internalization (WBI), the process of internalizing negative attitudes and stereotypes towards overweight individuals, significantly impacts self-worth and health behaviors, such as exercise avoidance. In the current study, we focused on the mediating role of fitness-related self-conscious emotions, particularly shame and guilt. A cross-sectional study involving 150 self-described overweight Dutch women (age M = 49.63 ± 10.72) was conducted online. Participants completed measures assessing weight bias internalization, exercise avoidance, and body/fitness-related self-conscious emotions. Data were analyzed using linear regression and mediation analysis, controlling for age, BMI, and exercise frequency. The results show that weight bias internalization, guilt-free shame, and shame-free guilt uniquely predict exercise avoidance. Guilt-free shame partially mediated the relationship between weight bias internalization and exercise avoidance, indicating that increased internalized weight bias led to higher levels of guilt-free shame, which in turn contributed to exercise avoidance. Shame-free guilt did not act as a unique mediator. These findings underscore the importance of addressing weight bias internalization and fitness-related self-conscious emotions, particularly guilt-free shame, in interventions targeting exercise avoidance among overweight individuals. Strategies promoting self-compassion and reducing shame may prove beneficial in improving exercise behaviors and overall well-being.