Background: Young adult cancer survivors, defined as individuals aged 18–39 who have completed primary curative treatment, face numerous age-specific biopsychosocial late effects that impact health-related quality of life negatively. Rehabilitation can enhance participation in life roles, work, leisure activities and health-related quality of life. However, there is a lack of age-specific cancer rehabilitation for this population, leaving many young adults with diminished self-efficacy in managing their challenges, resulting in unmet needs. This study aimed to co-produce and develop an age-specific, municipality-based cancer rehabilitation intervention programme to improve young adults' self-efficacy and health-related quality of life. Methods: The development process was completed between September 2019 and June 2023 and followed Hawkins et al.'s three-staged framework for co-production: (1) A literature review and stakeholder consultations; (2) four workshops with 2–6 young adult cancer survivors, 3–4 professionals, and two researchers and one workshop with 20 young adult cancer survivors and two researchers to co-produce the name, component content, delivery methods and potential outcomes; and (3) Refinement of the programme and its programme theory. Key findings from each stage informed the subsequent stages. Results: The Young Adults Taking ACtion programme was developed. It applies a person-centred approach and is grounded in social cognitive theory and experiential learning theory. It comprises one mandatory component, a needs assessment and goal setting that tailor which of the following seven components the young adults will receive: (1) everyday life, (2) physical activity, (3) psychological issues, (4) education and work, (5) sexuality and relationships, (6) funds and grants, and (7) family and friends. The programme is primarily group-based and will be delivered by an interdisciplinary team over 16 weeks. Conclusions: We co-produced a comprehensive, goal-oriented, and peer-based rehabilitation programme for young adult cancer survivors. The engagement of young adults and professionals ensured that the programme aligned with the population's needs and preferences and was context specific. Thus, it is likely that the programme will be more realistic and feasible to implement in clinical practice. Plain English Summary: Young adult cancer survivors, defined as persons aged 18–39 who have completed primary curative treatment, constitute a unique group, as they are in a particular life phase forming the foundations of their lives. As a result, they face distinct age-specific challenges in their everyday life related to education, work, and social activities, which negatively impact their quality of life. Rehabilitation may address these challenges, however there is a lack of rehabilitation programmes specifically tailored for young adult cancer survivors. This paper describes the co-production and development of an age-specific and municipality-based cancer rehabilitation programme to improve young adult cancer survivors' self-efficacy and health-related quality of life. The development included the following steps: (1) reviewing existing literature on cancer rehabilitation programmes for young adults and consulting with relevant stakeholders to gain insights into the target population and the context for implementation; (2) conducting four workshops involving 2–6 young adults, 3–4 professionals, and two researchers and one workshop with 20 young adults and two researchers to co-produce the programmes name, component content, delivery methods, and potential outcomes; and (3) Refine of the programme description. The co-produced programme, Young Adults Taking ACtion, includes one mandatory session for needs identification and goal setting that guides which of the following sessions the young adult cancer survivors will receive: (1) Everyday life, (2) Physical activity, (3) Psychological issues, (4) Education and work, (5) Sexuality and relationships, (6) Funding and grant, and (7) Family and friends. [ABSTRACT FROM AUTHOR]