This study sought to understand how advocacy as a public relations activity can give voice to marginalized publics and how/if mental health advocates perceive their advocacy work as influencing culture as it relates to mental health. This study incorporated the theoretical frameworks of fully functioning society theory (FFST) and the circuit of culture. Additionally, this study investigated the concepts of advocacy, legitimacy, cultural intermediation and discourses as they entangle with and within FFST and the circuit of culture. The juxtaposition of these theories helped to uncover both culturally situated best practices of advocacy and interrogate the frames that underpin the rhetorical ideals of a fully functioning society. This study employed qualitative, in-depth interviews with 38 mental health advocates who communicated a variety of perspectives about mental health and illness. Some themes that emerged include: advocacy as both education and empowerment, legitimacy as authority that can derive from both lived and learned experience, the multiple subcultures within the field of mental health advocacy, and the variety of mental health discourses. Furthermore, two overlapping, but distinct missions of advocacy exist including 1) general mental health for all of society and 2) advocacy for people who have experienced significant challenges to daily life and/or harm (e.g., prejudice, discrimination) because of a psychiatric diagnosis. This dissertation extended FFST and the circuit of culture to present a culturally embedded conceptual model of advocacy and theoretical propositions to help guide future theory building. The theoretical propositions outline how advocacy is a vehicle for voice to change status quos, how dysfunction and marginality are parallel within FFST, and how legitimation and cultural intermediation align in the context of culturally situated responsible advocacy. The findings also contributed to the existing theories by applying those theories to a specific context of mental health advocacy, which illuminated the importance of questioning normalized values within FFST and approaching intermediation with reflectiveness. This research considers the consequences of advocacy for people with lived experiences and situates advocacy within social justice contexts to inch closer towards the ideals of FFST.