Objective: This study aimed: (1) to compare psychological distress (PD) and body dissatisfaction (BD) in terms of BMI, weight bias internalization (WBI), and weight discrimination (current and past); (2) to assess the best predictor of PD and BD and assess the relationships with weight discrimination, BD, and WBI. Methods: The sample consisted of 1283 participants across all BMI categories, recruited through the internet voluntarily. People with obesity were the most predominant (26.1%). Experiences of weight-based discrimination were reported by participants across all BMI categories, and they were more prevalent in people with obesity. Results: People with obesity, those with WBI, and those who faced current and past weight discrimination reported higher PD and higher BD. However, WBI was the best predictor after controlling for BMI, WBI, and current and past weight discrimination. Mediation analyses revealed that the relationship between weight discrimination and BD through WBI was significant, as was the relationship between weight discrimination and WBI through BD. Conclusions: These results stressed the importance of WBI in PD and the role of weight discrimination in WBI and BD. Hence, there is a need to better understand how WBI is formed and to design effective interventions to reduce it.