This qualitative study delves into consumer perceptions and behaviors toward sustainable fashion in the UK, with a focus on how these attitudes shape brand legitimacy. Drawing on principles of sustainability and the circular economy, the research explores the nuanced relationship between sustainable practices, consumer trust, and brand legitimacy in the fashion industry. Through in-depth interviews with young adults, specifically Gen Z university students, the study seeks to uncover the underlying motivations and values driving their engagement with sustainable fashion. Thematic analysis is employed to identify key themes and patterns in participants’ responses. The findings shed light on the importance of aligning brand values with sustainability to build consumer trust and foster long-term brand relationships.