Polycystic ovary syndrome (PCOS) represents a significant global health burden requiring urgent attention. This common chronic endocrine and cardiometabolic condition affects around 1 in 10 women and individuals assigned female at birth, with significant adverse effects on well-being, quality of life, and mental health, as well as serious and complex long-term health consequences. International guidelines for best health care practice recommend the provision of comprehensive cognitive behavioral interventions to support self-management and improve health outcomes for those living with PCOS. Web-based health interventions have the potential to meet this need in an accessible and scalable way. We aim to identify barriers to self-management and psychological well-being in women with PCOS and adapt a web-based self-management program to provide a prototype digital support intervention for them. We adapted an existing support program (HOPE) for PCOS using the antecedent target measure approach. We conducted qualitative interviews with 13 adult women living with PCOS, 3 trustees of a patients with PCOS advocacy charity, and 4 endocrinologists to identify "antecedents" (barriers) to self-management and psychological well-being. Framework analysis was used to identify potentially modifiable antecedents to be targeted by the novel intervention. At a national conference, 58 key stakeholders (patients and health professionals) voted for the antecedents they felt were most important to address. We used research evidence and relevant theory to design a prototype for the PCOS intervention. Voting identified 32 potentially modifiable antecedents, relating to knowledge, understanding, emotions, motivation, and behaviors, as priorities to be targeted in the new intervention. A modular, web-based prototype HOPE PCOS intervention was developed to address these, covering six broad topic areas (instilling HOPE for PCOS; managing the stress of PCOS; feeding your mind and body well; body image, intimacy, and close relationships; staying healthy with PCOS; and keeping PCOS in its place). We identified barriers to self-management and psychological well-being in women with PCOS and used these to adapt a web-based self-management program, tailoring it for PCOS, which is a comprehensive group intervention combining education, empowerment, lifestyle management, peer support with cognitive behavioral tools, and goal-setting (to be delivered by peers or codelivered with health care professionals). The modular structure offers flexibility to adapt the program further as new clinical recommendations emerge. The intervention has the potential to be delivered, evaluated for feasibility, and, if effective, integrated into health care services. Self-management interventions are not designed to replace clinical care; rather, they serve as an additional source of support. The HOPE PCOS program conveys this message in its content and activities. Future research should evaluate the prototype intervention using primary outcomes such as measures of psychological well-being, self-management self-efficacy, depression, anxiety, and PCOS-related quality of life. They should also assess the intervention's acceptability, scalability, and cost-effectiveness.