(1) Background: There is a fundamental shift in healthcare toward shared decision making (SDM). This study explores SDM from the perspective of individuals affected by mental illness and their family members and investigates factors which promote and hinder the process. (2) Methods: We conducted N = 15 telephone interviews (n = 4 adults affected by mental illness, n = 5 family members, n = 6 both applicable, the majority reporting experiences with affective and anxiety disorders). Data were recorded, transcribed, and analyzed according to procedures established by Mayring. (3) Results: Individuals affected by mental illness and their family members have a strong desire to be involved in treatment decisions and to participate in finding a diagnosis. Often these stakeholders are denied the opportunity to participate; sometimes enabling behaviors impede participation. The stigmatization of mental illnesses is a major barrier. There are also structural barriers to SDM within the healthcare system. Peer support, self-help associations, and psychosocial counseling services are important to empowering individuals and promoting SDM. (4) Conclusions: SDM has the potential to improve the quality of mental healthcare. Barriers can be mitigated and new approaches for interventions in the psychiatric sector have been identified. This study has also shown the importance of understanding SDM as a process that should begin at the diagnostic phase.