With a reputation for offering stylish and on-trend clothing at pocket-friendly prices, fast fashion brands resonate with the economic realities faced by many Gen Z consumers. Gen Z consumers are not just a target consumer market but also a driving force shaping the future of the fashion industry. Their preferences, values, and behaviors impact trends, reshape retail practices, and influence the overall trajectory of the fashion landscape. The evolving discourse surrounding sustainability and conscious consumerism suggests that the future may see a recalibration of the fashion landscape, with Gen Z at the forefront of demanding more responsible and transparent practices from the fashion industry. Therefore, this study aimed to identify the factors significantly influencing U.S. Gen Z consumers’ intentions to purchase fast fashion. Building on the theory of planned behavior, a research model for understanding Gen Z consumers’ intentions to buy fast fashion is proposed. Attitude, subjective norms, perceived behavioral control, environmental knowledge, need for uniqueness, materialism, and fashion leadership are investigated as predictors. Moreover, we examined how environmental knowledge, need for uniqueness, materialism, and fashion leadership affect Gen Z consumers’ attitudes toward fast fashion products. A total of 528 eligible responses were collected for analysis through a Qualtrics online survey. The proposed model’s psychometric properties were evaluated, and the hypotheses were tested using the multiple regression method. It was found that attitude, perceived consumer effectiveness, environmental knowledge, and fashion leadership significantly influenced Gen Z consumers’ intentions to shop fast fashion. Additionally, Gen Z consumers’ environmental knowledge, need for uniqueness, and fashion leadership significantly affect their attitudes toward fast fashion. The research model demonstrated strong explanatory power, explaining 68.9% of the variance in Gen Z consumers’ purchase intention toward fast fashion.